Encoder system, signal processing method, and transmission signal generation and output device

ABSTRACT

An encoder system includes: a first single-rotation absolute encoder that outputs a first signal corresponding to an angular position of a first rotatable shaft; a power transmission device that transmits the power of the first shaft to a second rotatable shaft with a predetermined transmission ratio; a second single-rotation absolute encoder that outputs a second signal corresponding to an angular position of the second shaft; and a signal processing section that generates data related to the rotation count of the first shaft based on at least the first signal and the second signal.

This is a Continuation Application of International Application No.PCT/JP2009/004126, filed Aug. 26, 2009, which claims priority toJapanese Patent Application Nos. 2008-216773 filed on Aug. 26, 2008,2008-233793 filed on Sep. 11, 2008, 2008-258603 filed on Oct. 3, 2008,2008-271628 filed on Oct. 22, 2008, and 2009-092036 filed on Apr. 6,2009, the contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to an encoder system as a control systemwhich includes an actuator such as an AC servo motor, for example, usedin industrial robots, a position sensor such as an encoder for detectingthe positional displacement of the actuator, and a controller.

2. Description of Related Art

Conventionally, in an encoder system, an encoder was generally disposedon an input shaft side of a motor, and it was necessary to use amultiple-rotation absolute encoder having an external battery in orderto obtain multiple-rotation information (namely, multiple-rotation data)which represents the number of rotations of a shaft of the motor. As anexample of such conventional art, Japanese Patent Application,Publication No. H04-025388 A is known.

Moreover, as an example of an encoder system (encoder device) of theconventional art, there is known an encoder system in which a planetaryreduction gear, for example, is disposed on an output shaft of a servomotor having an encoder mounted thereon, and a servo driver controls theservo motor based on a rotation command signal. There is also known atechnique in which, when the planetary reduction gear has a transmissionangle error, a rotation angle error of the planetary reduction gear andthe input rotation command signal are corrected using an inputsynchronization correction circuit (for example, see Japanese PatentApplication, Publication No. H09-311725 A).

SUMMARY

As described above, in the conventional art, when a robot is notoperated, and a main power supply (+5 V) is OFF, in order to keep trackof an absolute position, an encoder system using the multiple-rotationabsolute encoder needed to have an external battery for storing theabsolute position information. Moreover, it was necessary to supply avery small current constantly to the encoder from the external battery.

The external battery has to be replaced for every predetermined periodmainly as a part of periodic maintenance, which is a great limitationduring the maintenance.

That is, in the maintenance of such an encoder system, it is generallynecessary to set a predetermined period in advance with a sufficientmargin with respect to the MTBF (Mean Time Between Failure) of aconsumable component and perform replacement of the external battery,for example, as so-called “periodic maintenance.”

A purpose of aspects of the present invention is to provide an encodersystem and a signal processing method capable of obtainingmultiple-rotation information without using an external battery.

According to an aspect of the present invention, there is provided anencoder system including: a motor that rotates an input shaft; a firstabsolute position encoder that is a single-rotation absolute encoder andthat outputs a first detection signal corresponding to a positionaldisplacement in the rotation of the input shaft; a power transmissiondevice that rotates an output shaft at a predetermined transmissionratio in response to the rotation of the input shaft; a second absoluteposition encoder that is a single-rotation absolute encoder and thatoutputs a second detection signal corresponding to a positionaldisplacement in the rotation of the output shaft; and a signalprocessing circuit that processes the first and second detection signalscorresponding to the positional displacements detected by the first andsecond absolute position encoders, wherein the signal processing circuitincludes: a first position data detection circuit that detects firstposition data representing the positional displacement in the rotationof the input shaft through first predetermined signal processing basedon the first detection signal input from the first absolute positionencoder; a second position data detection circuit that detects secondposition data representing the positional displacement in the rotationof the output shaft through second predetermined signal processing basedon the second detection signal input from the second absolute positionencoder; a position data combination circuit that combines the firstposition data detected by the first position data detection circuit andthe second position data detected by the second position data detectioncircuit to generate combined position data representing the number ofrotations of the input shaft and the positional displacement within onerotation of the input shaft; and a position data comparing and collatingcircuit that compares and collates the first position data detected bythe first position data detection circuit and the second position datadetected by the second position data detection circuit.

According to another aspect of the present invention, there is provideda signal processing method used in an encoder system which includes: amotor that rotates an input shaft; a first absolute position encoderthat is a single-rotation absolute encoder and that outputs a firstdetection signal corresponding to a positional displacement in therotation of the input shaft; a power transmission device that rotates anoutput shaft at a predetermined transmission ratio in response to therotation of the input shaft; a second absolute position encoder that isa single-rotation absolute encoder and that outputs a second detectionsignal corresponding to a positional displacement in the rotation of theoutput shaft; and a signal processing circuit that processes the firstand second detection signals corresponding to the positionaldisplacements detected by the first and second absolute positionencoders, wherein the signal processing circuit performing processingincluding: a first position data detection step of detecting firstposition data representing the positional displacement in the rotationof the input shaft through first predetermined signal processing basedon the first detection signal input from the first absolute positionencoder; a second position data detection step of detecting secondposition data representing the positional displacement in the rotationof the output shaft through second predetermined signal processing basedon the second detection signal input from the second absolute positionencoder; a position data combination step of combining the firstposition data detected in the first position data detection step and thesecond position data detected in the second position data detection stepto generate combined position data representing the number of rotationsof the input shaft and a positional displacement within one rotation ofthe input shaft; and a position data comparing and collating step ofcomparing and collating the first position data detected in the firstposition data detection step and the second position data detected inthe second position data detection step.

According to a further aspect of the present invention, there isprovided an encoder system including: a motor that rotates an inputshaft; a first absolute position encoder that is a single-rotationabsolute encoder and that outputs a first detection signal correspondingto an angular position of the input shaft; a power transmission devicethat rotates an output shaft at a predetermined transmission ratio inresponse to the rotation of the input shaft; a second absolute positionencoder that is a single-rotation absolute encoder and that outputs asecond detection signal corresponding to an angular position of theoutput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection circuit that detects second position datarepresenting the angular position of the output shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; a transmission signalgeneration and output section that generates and outputs a transmissionsignal corresponding to the rotation of the input shaft based on thesecond position data detected by the second position data detectioncircuit; and a position data combination circuit that measures arotation count of the input shaft based on the transmission signal inputfrom the transmission signal generation and output section and combinesthe measured rotation count and the first position data detected by thefirst position data detection circuit to generate combined position datarepresenting the rotation count of the input shaft and the angularposition of the input shaft.

According to a still further aspect of the present invention, there isprovided a signal processing method used in an encoder system whichincludes: a motor that rotates an input shaft; a first absolute positionencoder that is a single-rotation absolute encoder and that outputs afirst detection signal corresponding to an angular position of the inputshaft; a power transmission device that rotates an output shaft at apredetermined transmission ratio in response to the rotation of theinput shaft; and a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of the output shaft, themethod including the steps of: detecting first position datarepresenting the angular position of the input shaft through firstpredetermined signal processing based on the first detection signalinput from the first absolute position encoder; detecting secondposition data representing the angular position of the input shaftthrough second predetermined signal processing based on the seconddetection signal input from the second absolute position encoder;generating and outputting a transmission signal corresponding to therotation of the input shaft based on the second position data detectedby the second position data detection circuit; and measuring a rotationcount of the input shaft based on the input transmission signal andcombining the measured rotation count and the first position datadetected by the first position data detection circuit to generatecombined position data representing the rotation count of the inputshaft and the angular position of the input shaft.

According to a still further aspect of the present invention, there isprovided a transmission signal generation and output device used in anencoder system which includes: a motor that rotates an input shaft; afirst absolute position encoder that is a single-rotation absoluteencoder and that outputs a first detection signal corresponding to anangular position of the input shaft; a power transmission device thatrotates an output shaft at a predetermined transmission ratio inresponse to the rotation of the input shaft; a second absolute positionencoder that is a single-rotation absolute encoder and that outputs asecond detection signal corresponding to an angular position of theoutput shaft, in which the encoder system combines the first positiondata detected by the first position data detection circuit and atransmission signal input thereto to generate combined position datarepresenting the rotation count of the input shaft and the angularposition of the input shaft, wherein the transmission signal generationand output device generates and outputs a transmission signalcorresponding to the rotation of the input shaft based on the secondposition data detected by the second position data detection circuit.

According to a still further aspect of the present invention, there isprovided an encoder system including: a motor that rotates an inputshaft; a first absolute position encoder that is a single-rotationabsolute encoder and that outputs a first detection signal correspondingto an angular position of the input shaft; a power transmission devicethat rotates an output shaft at a predetermined transmission ratio inresponse to the rotation of the input shaft; a second absolute positionencoder that is a single-rotation absolute encoder and that outputs asecond detection signal corresponding to an angular position of theoutput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection circuit that detects second position datarepresenting the angular position of the input shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; a position datacombination circuit that combines the first position data detected bythe first position data detection circuit and the second position datadetected by the second position data detection circuit to generatecombined position data representing a multiple-rotation count of theinput shaft and the angular position within one rotation of the inputshaft; and a rotation direction detection section that detects whether arotation direction of the input shaft detected based on the displacementof the first position data and a rotation direction of the output shaftdetected based on the displacement of the second position data are thesame directions or reverse directions.

According to a still further aspect of the present invention, there isprovided a signal processing method used in an encoder system whichincludes: a motor that rotates an input shaft; a first absolute positionencoder that is a single-rotation absolute encoder and that outputs afirst detection signal corresponding to an angular position of the inputshaft; a power transmission device that rotates an output shaft at apredetermined transmission ratio in response to the rotation of theinput shaft; and a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of the output shaft, themethod including: a first position data detection step of detectingfirst position data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection step of detecting second position datarepresenting the angular position of the input shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; a position datacombination step of combining the first position data detected in thefirst position data detection step and the second position data detectedin the second position data detection step to generate combined positiondata representing a multiple-rotation count of the input shaft and theangular position within one rotation of the input shaft; and a rotationdirection detection step of detecting whether a rotation direction ofthe input shaft detected based on the displacement of the first positiondata and a rotation direction of the output shaft detected based on thedisplacement of the second position data are the same directions orreverse directions.

According to a still further aspect of the present invention, there isprovided an encoder system including: a motor that rotates an inputshaft; a controller that controls the rotation of the motor using arotation control signal; a first absolute position encoder that is asingle-rotation absolute encoder and that outputs a first detectionsignal corresponding to an angular position of the input shaft; a powertransmission device that rotates an output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft; asecond absolute position encoder that is a single-rotation absoluteencoder and that outputs a second detection signal corresponding to anangular position of the output shaft; a first position data detectioncircuit that detects first position data representing the angularposition of the input shaft through first predetermined signalprocessing based on the first detection signal input from the firstabsolute position encoder; a second position data detection circuit thatdetects second position data representing the angular position of theinput shaft through second predetermined signal processing based on thesecond detection signal input from the second absolute position encoder;a position data combination circuit that combines the first positiondata detected by the first position data detection circuit and thesecond position data detected by the second position data detectioncircuit to generate combined position data representing amultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft; and a failure detection sectionthat compares an input shaft angular position which is the angularposition of the input shaft calculated based on the rotation controlsignal from the controller and the first position data detected by thefirst position data detection circuit and compares an output shaftangular position which is the angular position of the output shaftcalculated based on the rotation control signal from the controller andthe second position data detected by the second position data detectioncircuit to detect a failure in accordance with a combination of thecomparison results.

According to a still further aspect of the present invention, there isprovided a signal processing method used in an encoder system whichincludes: a motor that rotates an input shaft; a controller thatcontrols the rotation of the motor using a rotation control signal; afirst absolute position encoder that is a single-rotation absoluteencoder and that outputs a first detection signal corresponding to anangular position of the input shaft; a power transmission device thatrotates an output shaft at a predetermined transmission ratio inresponse to the rotation of the input shaft; a second absolute positionencoder that is a single-rotation absolute encoder and that outputs asecond detection signal corresponding to an angular position of theoutput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection circuit that detects second position datarepresenting the angular position of the input shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; and a signal processingsection that processes the rotation control signal from the controller,the first position data detected by the first position data detectioncircuit, and the second position data detected by the second positiondata detection circuit, wherein the signal processing circuit performingprocessing including: a position data combination step of combining thefirst position data detected in the first position data detection stepand the second position data detected in the second position datadetection step to generate combined position data representing amultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft; and a failure detection step ofcomparing an input shaft angular position which is the angular positionof the input shaft calculated based on the rotation control signal fromthe controller and the first position data detected by the firstposition data detection circuit and comparing an output shaft angularposition which is the angular position of the output shaft calculatedbased on the rotation control signal from the controller and the secondposition data detected by the second position data detection circuit todetect a failure in accordance with a combination of the comparisonresults.

According to a still further aspect of the present invention, there isprovided an encoder system including: a first absolute position encoderthat is a single-rotation absolute encoder and that outputs a firstdetection signal corresponding to an angular position of a rotatinginput shaft; a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of an output shaft rotatingat a predetermined transmission ratio in response to the rotation of theinput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection circuit that detects second position datarepresenting the angular position of the input shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; a position datacombination circuit that combines the first position data and the secondposition data to generate combined position data representing amultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft; an error correction valuestorage section in which an error correction value for correcting thecombined position data is stored in advance, the error correction valuebeing a value which is obtained by driving an entire power transmissiondevice that rotates the output shaft in advance in a state where theentire power transmission device is incorporated into the encodersystem; and an error correction circuit that corrects the combinedposition data to be generated by the position data combination circuitbased on the error correction value read out from the error correctionvalue storage section.

According to a still further aspect of the present invention, there isprovided a signal processing method used in an encoder system whichincludes: a first absolute position encoder that is a single-rotationabsolute encoder and that outputs a first detection signal correspondingto an angular position of a rotating input shaft; a second absoluteposition encoder that is a single-rotation absolute encoder and thatoutputs a second detection signal corresponding to an angular positionof an output shaft rotating at a predetermined transmission ratio inresponse to the rotation of the input shaft; a first position datadetection circuit that detects first position data representing theangular position of the input shaft through first predetermined signalprocessing based on the first detection signal input from the firstabsolute position encoder; and a second position data detection circuitthat detects second position data representing the angular position ofthe input shaft through second predetermined signal processing based onthe second detection signal input from the second absolute positionencoder, in which: a position data combination circuit combines thefirst position data and the second position data to generate combinedposition data representing a multiple-rotation count of the input shaftand the angular position within one rotation of the input shaft; and anerror correction circuit corrects the combined position data to begenerated by the position data combination circuit based on an errorcorrection value read out from an error correction value storage sectionin which the error correction value for correcting the combined positiondata is stored in advance, the error correction value being a valuewhich is obtained by driving an entire power transmission device thatrotates the output shaft in advance in a state where the entire powertransmission device is incorporated into the encoder system.

According to a still further aspect of the present invention, there isprovided an encoder system including: a first single-rotation absoluteencoder that outputs a first signal corresponding to an angular positionof a first rotatable shaft; a power transmission device that transmitsthe power of the first shaft to a second rotatable shaft with apredetermined transmission ratio; a second single-rotation absoluteencoder that outputs a second signal corresponding to an angularposition of the second shaft; and a signal processing section thatgenerates data related to the rotation count of the first shaft based onat least the first signal and the second signal.

According to the some aspects of the present invention, it is possibleto provide an encoder system and a signal processing method capable ofobtaining multiple-rotation information without using an externalbattery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of an encoder systemaccording to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an encoder in theencoder system shown in FIG. 1.

FIG. 3 is a block diagram showing a configuration of a signal processingcircuit in the encoder system shown in FIG. 1.

FIG. 4 is a diagram illustrating the operation of an exemplary positiondata combination circuit and an exemplary position data comparing andcollating circuit.

FIG. 5 is a block diagram showing a configuration of an encoder systemaccording to another embodiment.

FIG. 6 is a block diagram showing a configuration of a signal processingcircuit in the encoder system shown in FIG. 5.

FIG. 7 is a waveform diagram showing the waveform of an exemplarybiphasic pseudo-sinusoidal wave and the like.

FIG. 8 is a waveform diagram showing the relationship between a seconddetection signal and second position data in one phase interval of FIG.7.

FIG. 9 is a schematic diagram showing a shift between the rotation countof an input shaft and the position data of the input shaft calculatedbased on the position data of an output shaft.

FIG. 10 is a table showing a rotation count correction method by asecond position data correction circuit when there is a shift.

FIG. 11 is a waveform diagram showing the waveform of an exemplarytransmission signal output to the second position data correctioncircuit by a transmission signal generation and output section.

FIG. 12 is a waveform diagram showing the waveform of an exemplarytransmission signal output to the second position data correctioncircuit by the transmission signal generation and output section at thetime of startup.

FIG. 13 is a flowchart showing the operation of the encoder system.

FIG. 14 is a diagram illustrating combined position data generated bythe encoder system.

FIG. 15 is a diagram showing a configuration for improving thereliability and stability of the encoder system.

FIG. 16 is a diagram illustrating a combined position in an encodersystem according to the conventional art when there is no shift.

FIG. 17 is a diagram illustrating a combined position in an encodersystem according to the conventional art when there is a shift.

FIG. 18 is a block diagram showing a configuration of a signalprocessing circuit in an encoder system according to another embodiment.

FIG. 19 is a waveform diagram showing a biphasic signal and the likewhen the rotation direction of an input shaft is identical to therotation direction of an output shaft.

FIG. 20 is a table showing the correction method in the case of FIG. 19.

FIG. 21 is a waveform diagram showing a biphasic signal and the likewhen the rotation direction of an input shaft is reverse to the rotationdirection of an output shaft.

FIG. 22 is a table showing the correction method in the case of FIG. 19.

FIG. 23 is a table illustrating a method of detecting a rotationdirection from a biphasic signal.

FIG. 24 is a block diagram showing a configuration of an encoder systemaccording to another embodiment.

FIG. 25 is a block diagram showing a configuration of a signalprocessing circuit in the encoder system.

FIG. 26 is a diagram illustrating the operation of an exemplary positiondata combination circuit and an exemplary position data comparing andcollating circuit.

FIG. 27 is a block diagram showing a configuration of a signalprocessing circuit in an encoder system according to another embodiment.

FIG. 28 is a diagram showing a rotation angle error of a first encoder 3on the input shaft with respect to the rotation angle of a secondencoder 4 on the output shaft.

FIG. 29 is a block diagram showing a configuration of an encoder systemwhen an error correction value is obtained by a second method.

FIG. 30 is a block diagram showing an encoder system having a differentconfiguration from that shown in FIG. 1.

FIG. 31 is a block diagram showing a configuration of a signalprocessing circuit in the encoder system shown in FIG. 30.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. FIG. 1 is a schematic block diagram showing aconfiguration of an encoder system according to an embodiment of thepresent invention.

In the present embodiment, an encoder system includes a motor 1, a powertransmission device 2, a first encoder (first absolute position encoder)3, a second encoder (second absolute position encoder) 4, an input shaft(first shaft) 10, and an output shaft (second shaft) 11. Moreover, theencoder system includes a controller 8 which is a high-order device anda communication line 9 which is a communication line between thecontroller 8 and the first encoder 3. In addition, the first encoder 3and the second encoder 4 are connected at least through a communicationline 12.

The motor 1 rotates the input shaft 10 in accordance with a rotationcontrol signal input from the controller 8. The power transmissiondevice 2 rotates the output shaft 11 by reducing the rotation speed ofthe output shaft 11 at a predetermined transmission ratio (powertransmission ratio) in response to the rotation of the input shaft 10.The power of the input shaft 10 is transmitted to the output shaft 11 ata predetermined transmission ratio through the power transmission device2.

That is, in this encoder system, the motor 1 rotates to the input shaft10, and in response to the rotation of the input shaft 10, the outputshaft 11 is rotated by the power transmission device 2. The powertransmission device 2 includes, for example, one or plural gears, beltdevices, chain devices, and drive shaft devices or a combination ofthese gears and devices.

The first encoder 3 is a single-rotation absolute encoder and outputs afirst detection signal corresponding to a positional displacement (anangular position of the input shaft 10) in the rotation of the inputshaft 10. The encoder converts a mechanical displacement amount in therotation direction into a digital amount.

That is, the first encoder 3 is a single-rotation absolute encoder whichhas a function of detecting the angular position of the input shaft 10of the motor 1 and is capable of detecting the position in terms of themechanical angle 360°. The single-rotation absolute encoder is anencoder which is not capable of detecting so-called “multiple-rotationdata/multiple-rotation information” representing “how many times a shafthas rotated” as rotation information.

The second encoder 4 is a single-rotation absolute encoder similarly tothe first encoder 3 and outputs a second detection signal correspondingto the positional displacement (the angular position of the output shaft11) in the rotation of the output shaft 11.

The first encoder 3 and the second encoder 4 include, for example, arotating disc which has N and S poles and which rotates in response tothe rotation of a corresponding shaft among the input shaft 10 and theoutput shaft 11 and two Hall-effect elements as magnetic sensor deviceswhich are disposed at predetermined positions so that the mutual angleis at 90° with respect to the rotation center axis of the rotating disc.

When the input shaft 10 or the output shaft 11 rotates, the rotatingdisc corresponding to the rotating shaft rotates as a rotary magnethaving the N and S poles, whereby a sinusoidal signal of which one pulseperiod corresponds to one rotation is output from the Hall-effectelements. Since the Hall-effect elements are disposed so as to have amutual angle of 90°, a sinusoidal wave having a phase difference of 90°,namely a so-called biphasic pseudo-sinusoidal wave is output as thesinusoidal signal.

In this way, the first encoder 3 outputs a biphasic sinusoidal signal,which is made up of two sinusoidal signals of which one cyclecorresponds to one rotation of the input shaft 10 and of which thephases are different by an amount of a predetermined phase, for example,as the first detection signal. Moreover, similarly to the first encoder3, the second encoder 4 outputs a biphasic sinusoidal signal, which ismade up of two sinusoidal signals of which one cycle corresponds to onerotation of the output shaft 11 and of which the phases are different byan amount of a predetermined phase, for example, as the second detectionsignal.

Here, for example, it is assumed that the first encoder 3 outputs Nsignals for one rotation, the second encoder 4 outputs M signals for onerotation, and the power transmission device 2 connects the input shaft10 and the output shaft 11 at a ratio of 1:N. In this case, since thesecond encoder 4 rotates by one digit whenever the first encoder 3 makesone rotation, it is possible to detect the rotation count of the inputshaft 10 and to detect the positional displacement (angular position) inthe rotation of the input shaft 10. Therefore, this encoder system iscapable of detecting N×M rotational positions, namely the absoluteposition in the rotation of the input shaft 10 until the output shaft 11makes M rotations.

That is, this encoder system functions as a multiple-rotation absoluteencoder as the whole encoder system using the first encoder 3 which is asingle-rotation absolute encoder and the second encoder 4 which is asingle-rotation absolute encoder. Therefore, this encoder system doesnot require an external battery for storing the absolute positioninformation which was required in the encoder system of the conventionalart.

In the present embodiment, the first encoder 3 has a signal processingcircuit 6 therein. The signal processing circuit 6 receives the seconddetection signal detected by the second encoder 4 through thecommunication line 12. Then, the signal processing circuit 6 detectscombined position data representing the number of rotations of the inputshaft 10 and the positional displacement (angular position) within onerotation of the input shaft 10 based on the first detection signaldetected by the first encoder 3 and the second detection signal detectedby the second encoder 4. Moreover, the signal processing circuit 6detects a failure or the like based on the first detection signal andthe second detection signal and uses the detection result as errorstatus information. Then, the signal processing circuit 6 outputs thedetected combined position data and the error status information to thecontroller 8 through the communication line 9.

In this way, the controller 8 is able to detect the number of rotationsof the input shaft and the positional displacement (angular position)within one rotation of the input shaft 10 based on the combined positiondata from the encoder system serving as the multiple-rotation absoluteencoder. Moreover, the controller 8 is able to detect a failure of theencoder system, for example, caused by abnormalities in the rotationmechanism of the motor 1, abnormalities in the power transmission device2, and abnormalities in a rotating disc 301 and a rotating disc 401,described later, which are included in the first encoder 3 or the secondencoder 4 based on the error status information.

Next, the configuration of the encoder system described using FIG. 1will be described in detail using FIGS. 2 and 3. In the drawings, thesame constituent elements as those in FIG. 1 will be denoted by the samereference numerals, and description thereof will be omitted. First, theconfiguration of the first and second encoders 3 and 4 will be describedusing FIG. 2.

<Configuration of First Encoder 3>

The first encoder 3 is a single-rotation absolute encoder which has afunction of detecting the positional displacement (angular position) inthe rotation of the input shaft of the motor 1 and is capable ofdetecting the position of a marker rotating with the rotation of theinput shaft in terms of the mechanical angle 360°. The first encoder 3is, for example, a single-rotation absolute encoder and is an opticalencoder.

A specific example of the configuration of the first encoder 3 will bedescribed. In the first encoder 3, the rotating disc 301 has aconfiguration in which an absolute pattern and an incremental patterndetermined by a predetermined M-series code are formed on a discrotating with the rotation of the input shaft 10. Light emitted from alight-emitting element 302 passes through the respective patterns on therotating disc 301 and enters a light-receiving sensor 303. Then, thelight-receiving sensor 303 outputs two signals including a signaldetected from the absolute pattern and a signal detected from theincremental pattern to the signal processing circuit 6 as the firstdetection signal.

One of the two signals output from the light-receiving sensor 303,specifically the signal detected from the absolute position is input tothe signal processing circuit 6 (specifically, an absolute positiondetection circuit 611 described later) as an absolute position detectionsignal (or an M-series signal).

Moreover, the other of the two signals output from the light-receivingsensor 303, specifically the signal detected from the incrementalpattern is input to the signal processing circuit 6 (specifically afirst interpolation circuit 612) as a first incremental signal (or abiphasic pseudo-sinusoidal wave).

<Configuration of Second Encoder 4>

The second encoder 4 has a function of detecting a displacementposition, namely position information in the rotation of the outputshaft 11 connected through the power transmission device 2 from theinput shaft 10 of the motor 1. The second encoder outputs apseudo-sinusoidal wave which has a phase difference of 90° and whichcauses a displacement of 1λ (≈phase angle: 360°) for one magneticrotation. The second encoder 4 is, for example, a single-rotationabsolute encoder and is a magnetic encoder. Therefore, the secondencoder 4 has a simpler configuration and is cheaper than the firstencoder 3.

A specific example of the configuration of the second encoder 4 will bedescribed. The second encoder 4 has a rotating disc 401 in which thedisc surface is divided into N and S regions, namely a rotating disc 401having a magnetic pole configuration of N and S poles. The rotating disc401 rotates with the rotation of the output shaft 11.

A magnetic sensor device 402 is disposed on the rotating disc 401. Themagnetic sensor device 402 includes two magnetic sensors 403 and 404disposed on the circumference on which the rotating disc 401 rotates.The two magnetic sensors 403 and 404 are, for example, Hall-effectelements which are positioned at predetermined positions so that themutual angle is at 90° with respect to the rotation center axis of therotating disc 401.

The magnetic sensor device 402 outputs a sinusoidal signal of which onepulse period corresponds to one rotation in response to when therotating disc 401 having the N and S poles makes one rotation as arotary magnet. Since the magnetic sensor device 402 has the magneticsensors 403 and 404 having a mutual angle of 90°, a biphasicpseudo-sinusoidal wave (for example, biphasic signals of A-phase andB-phase signals) having a phase difference of 90° is output from themagnetic sensor device 402 by the respective magnetic sensors.

Moreover, the biphasic pseudo-sinusoidal wave output by the magneticsensor device 402 is input to the signal processing circuit 6(specifically, a second interpolation circuit 621 described later) asthe second detection signal, namely the second incremental signal.

<Configuration of Signal Processing Circuit 6>

Next, the configuration of the signal processing circuit 6 will bedescribed using FIG. 3. The signal processing circuit 6 includes a firstposition data detection circuit 61, a second position data detectioncircuit 62, a position data combination circuit 63, a position datacomparing and collating circuit 64, an external communication circuit65, a transmission ratio information storage section (transmission ratioinformation storage section) 66, a first resolution storage section 67,and a second resolution storage section 68.

In the transmission ratio information storage section 66, informationrepresenting the value of a predetermined transmission ratio (forexample, a gear ratio) of the power transmission device 2 connecting thefirst encoder 3 and the second encoder 4 is stored in advance astransmission ratio information (for example, gear ratio information). Inthe first resolution storage section 67, the resolution of the firstposition data detection circuit 61 is stored in advance as a firstresolution. In the second resolution storage section 68, the resolutionof the second position data detection circuit 62 is stored in advance asa second resolution.

The first position data detection circuit 61 detects first position datarepresenting the positional displacement (angular position) in therotation of the input shaft 10 through first predetermined signalprocessing based on the first detection signal input from thelight-receiving sensor 303.

The second position data detection circuit 62 detects second positiondata representing the positional displacement (angular position) in therotation of the output shaft 11 through second predetermined signalprocessing based on the second detection signal input from the magneticsensor device 402.

The position data combination circuit 63 combines the first positiondata detected by the first position data detection circuit 61 and thesecond position data detected by the second position data detectioncircuit 62 to generate combined position data representing the number ofrotations of the input shaft 10 and the positional displacement (angularposition) within one rotation of the input shaft 10. When combining thefirst position data detected by the first position data detectioncircuit 61 and the second position data detected by the second positiondata detection circuit 62, the position data combination circuit 63combines the combined position data based on the transmission ratioinformation read out from the transmission ratio information storagesection 66. Then, the position data combination circuit 63 outputs thegenerated combined position data to the controller 8 through thecommunication line 9 using the external communication circuit 65.

Specifically, when combining the first position data detected by thefirst position data detection circuit 61 and the second position datadetected by the second position data detection circuit 62, the positiondata combination circuit 63 combines the combined position data by apredetermined calculation method based on the transmission ratioinformation read out from the transmission ratio information storagesection 66, the first resolution read out from the first resolutionstorage section 67 and the second resolution read out from the secondresolution storage section 68.

The position data comparing and collating circuit 64 compares andcollates the first position data detected by the first position datadetection circuit 61 and the second position data detected by the secondposition data detection circuit 62. When comparing and collating thefirst position data detected by the first position data detectioncircuit 61 and the second position data detected by the second positiondata detection circuit 62, the position data comparing and collatingcircuit 64 performs the comparison and collation based on thetransmission ratio information read out from the transmission ratioinformation storage section 66. Then, the position data comparing andcollating circuit 64 outputs the result of comparison and collation tothe controller 8 through the communication line 9 using the externalcommunication circuit 65 as the error status information.

The position data comparing and collating circuit 64 compares andcollates the first position data detected by the first position datadetection circuit 61 and the second position data detected by the secondposition data detection circuit 62 through the following processing.

First, the position data comparing and collating circuit 64 calculatesposition data corresponding to the first position data to be detected bythe first position data detection circuit 61 as an estimate based on thesecond position data detected by the second position data detectioncircuit 62 and the transmission ratio information read out from thetransmission ratio information storage section 66. Specifically, theposition data comparing and collating circuit 64 calculates the estimatebased on the second position data detected by the second position datadetection circuit 62, the transmission ratio information read out fromthe transmission ratio information storage section 66, the firstresolution read out from the first resolution storage section 67, andthe second resolution read out from the second resolution storagesection 68.

Subsequently, the position data comparing and collating circuit 64calculates a difference between the calculated estimate and the firstposition data detected by the first position data detection circuit 61as an error estimate.

Then, the position data comparing and collating circuit 64 compares andcollates the first position data detected by the first position datadetection circuit 61 and the second position data detected by the secondposition data detection circuit 62 by determining whether or not thecalculated error estimate is within a predetermined range of values.Specifically, the position data comparing and collating circuit 64compares and collates the first position data detected by the firstposition data detection circuit 61 and the second position data detectedby the second position data detection circuit 62 by determining whetheror not the calculated error estimate is within a predetermined range ofvalues which are predetermined ratios determined for the firstresolution read out from the first resolution storage section 67.

Here, when making determination as to the calculated error estimate, theposition data comparing and collating circuit 64 uses a ratio of 1/4 orsmaller, for example, as the predetermined ratio determined for thefirst resolution read out from the first resolution storage section 67.This is to detect whether or not there is a shift of 1/4 cycle or morewhen the estimate, namely the estimated value of the first position datadetected by the first position data detection circuit 61 based on thesecond position data detected by the second position data detectioncircuit 62 is compared with the first position data actually detected bythe first position data detection circuit 61. The ratio of 1/4 used forcomparing with the absolute value of the calculated error estimatecorresponds to a 1/4 cycle. The value of the ratio may be set, forexample, to 1/8 so as to further decrease an allowable amount of theshift.

The external communication circuit 65 executes processing forcommunication with the controller 8 through the communication line 9.Moreover, the external communication circuit 65 stores the transmissionratio information received from the controller 8 through thecommunication line 9 in the transmission ratio information storagesection 66. Furthermore, the external communication circuit 65 storesthe first resolution received from the controller 8 through thecommunication line 9 in the first resolution storage section 67. Inaddition, the external communication circuit 65 stores the secondresolution received from the controller 8 through the communication line9 in the second resolution storage section 68.

<Configuration of First and Second Position Data Detection Circuits 61and 62>

The first position data detection circuit 61 includes an absoluteposition detection circuit 611, a first interpolation circuit 612, aposition detection circuit 613, and a conversion table storage section614. The second position data detection circuit 62 includes a secondinterpolation circuit 621.

In the conversion table storage section 614, an absolute positiondetection signal (M-series signal) and absolute position data which hasa predetermined resolution and which is information representing theabsolute position within one rotation of the input shaft are stored inadvance in a correlated manner. The absolute position data isinformation representing the absolute position in the rotation of theinput shaft 10.

The absolute position detection circuit 611 detects the absoluteposition data by converting (decoding) the absolute position detectionsignal input from the light-receiving sensor 303 with the aid of theconversion table storage section 614. That is, the absolute positiondetection circuit 611 converts the absolute position detection signalinto absolute position data by reading out absolute position datacorresponding to the absolute position detection signal input from thelight-receiving sensor 303 from the conversion table storage section614, thus detecting the absolute position data.

The first interpolation circuit 612 interpolates the first incrementalsignal input from the light-receiving sensor 303. That is, the firstinterpolation circuit 612 electrically segments the first incrementalsignal which is the biphasic pseudo-sinusoidal wave input from thelight-receiving sensor 303.

The position detection circuit 613 detects the first position data basedon the absolute position data output by the absolute position detectioncircuit 611 and the first incremental signal interpolated by the firstinterpolation circuit 612. Specifically, the position detection circuit613 calculates the first position data which is absolute position datahaving a higher resolution than the absolute position data detected bythe absolute position detection circuit 611 by combining the absoluteposition data detected by the absolute position detection circuit 611and the incremental signal segmented by the first interpolation circuit612 while ensuring consistency.

The second interpolation circuit 621 interpolates the second incrementalsignal input from the magnetic sensor device 402 of the second encoderdevice to detect the second position data. The second interpolationcircuit 621 generates the second position data which is absoluteposition information at a resolution close to or equal to the positionalresolution detected by the first encoder 3 through predeterminedinterpolation processing based on the second incremental signal which isthe biphasic pseudo-sinusoidal wave input from the magnetic sensordevice 402.

The number of segments produced by the second interpolation circuit 621is set to be a multiple of the transmission ratio of the powertransmission device 2 that connects the first encoder 3 and the secondencoder 4 (this multiple number is referred to as Np; where the multiplenumber Np is 2 or more). In addition, in order to realize a resolutionthat is close to or equal to the positional resolution of the firstencoder 3, it is necessary to increase the value of the multiple numberNp which is the factor of the second interpolation circuit 621 toincrease the resolution.

Moreover, the transmission ratio information which is information on thevalue of the transmission ratio of the power transmission device 2 canbe set from the outside (for example, through the communication line 9and the external communication circuit 65), and the set transmissionratio information is set and stored in the transmission ratioinformation storage section 66 included in the signal processing circuit6. The transmission ratio information storage section 66 is anonvolatile memory, for example. Therefore, once the transmission ratioinformation is set, it will not be erased even when the encoder systemis powered off. According to this configuration, it is possible tobroaden the choices for the power transmission device 2 and thetransmission ratio of the power transmission device 2 usable in theencoder system.

As described above, the second interpolation circuit 621 performsinterpolation by a predetermined method based on the transmission ratioinformation read out from the transmission ratio information storagesection 66 and the second incremental signal which is the biphasicpseudo-sinusoidal wave input from the magnetic sensor device 402 andgenerates the second position data which is absolute positioninformation at a resolution close to or equal to the positionalresolution detected by the first encoder 3.

The position data combination circuit 63 detects the number of rotationsof the input shaft of the motor 1, namely multiple-rotation informationof the first encoder 3 from the second position data obtained from thesecond encoder 4 and the transmission ratio information. This is becausethe quotient (integer part) when the second position data is divided bythe factor Np of the second interpolation circuit 621 corresponds to themultiple-rotation information of the first encoder 3.

The position data combination circuit 63 enables the multiple-rotationinformation of the first encoder to be known from the positioninformation of the second encoder without an external battery which wasnecessary mainly for storing the multiple-rotation information of themultiple-rotation absolute encoder of the conventional art.

That is, in the encoder system according to the present embodiment, theposition data combination circuit 63 combines the absolute positioninformation within one rotation obtained by the first encoder 3 and themultiple-rotation information obtained from the second encoder 4 whileensuring consistency whereby the encoder system can operate as amultiple-rotation absolute encoder which does not require a batterydevice.

In general, an external operation environment of a robot system using anAC servo motor to which encoders are often applied is very poor, and inmany cases, the robot system operates under an environment with manyelectrical disturbances such as high temperature and high humidity. Inparticular, as a problem concerning electronic circuits, there is apossibility of malfunction due to electric/magnetic field disturbances(commonly referred to as “noise”). Moreover, once the encoder systemmalfunctions, the production line must be stopped for a long period, andmalfunction due to noise may cause extremely extensive damages.

In the present embodiment, two systems of position data which are thefirst position data and the second data are constantly compared by theposition data comparing and collating circuit 64, and if there is afailure in any of the two systems, the result of comparison andcollation outputs a mismatch. Thus, it is possible to detect a problemin the encoder system.

Therefore, this encoder system can enhance the reliability of theposition information output from the first encoder 3 or the secondencoder 4 by the action of the position data comparing and collatingcircuit 64. Specifically, this encoder system is capable of detectingabnormalities in the rotation mechanism of the motor 1, abnormalities inthe power transmission device 2, and abnormalities of the rotating disc301 or the rotating disc 401 which is included in the first encoder 3 orthe second encoder 4. In addition, this encoder system is also capableof detecting the idle running of the rotating disc 301 or the rotatingdisc 401 as “abnormalities,” which is difficult to detect in the encodersystem of the conventional art.

Next, processing executed by the position data combination circuit 63and the position data comparing and collating circuit 64 will bedescribed in detail using FIG. 4. In this description, it is assumedthat the resolution of the first position data detection circuit 61,namely the resolution of the position detection circuit 613 is 13 bit,and the resolution of the second position data detection circuit 62 is11 bit. That is, the first position data detection circuit 61 outputsthe first position data which is an integer value within the range of 0to 8191 (=2¹³−1). Moreover, the second position data detection circuit62 outputs the second position data which is an integer value within therange of 0 to 2047 (=2¹¹−1). Moreover, it is assumed that thetransmission ratio of the power transmission device 2 is 100, and thetransmission ratio information having a value of 100 is stored inadvance in the transmission ratio information storage section 66.

Here, a case in which the first position data detection circuit 61outputs 1000 as the value of the first position data, and the secondposition data detection circuit 62 outputs 310 as the value of thesecond position data will be described as an example. Moreover, it isassumed that the rotation count of the input shaft 10 is 15.

First, the position data combination circuit 63 will be described. Theposition data combination circuit 63 calculates the combined positiondata using Equation 1 below.

Combined Position Data=P1+INT(n×P2/R2)  (Equation 1)

Here, P1 is the first position data, P2 is the second position data, andn is a transmission ratio. Moreover, R2 is the resolution of the secondposition data detection circuit 62. Moreover, INT is an operator thattruncates the fractional part and extracts only the integer part.

The position data combination circuit 63 calculates a value obtained byadding the value of the first position data (P1) to the value of theinteger part (INT) of a value obtained by multiplying a positional ratio(P2/R2) within one rotation of the second position data detectioncircuit 62 with the transmission ratio (n) as the combined position datausing Equation 1.

In this case, since the value of the first position data P1 is 1000, thevalue of the second position data P2 is 310, the value of thetransmission ratio n is 100, and the value of the resolution R2 of thesecond position data detection circuit 62 is 2048, the position datacombination circuit 63 calculates 123865 as the value of the combinedposition data using Equation 1.

Next, the position data comparing and collating circuit 64 will bedescribed. First, the position data comparing and collating circuit 64calculates the estimate using Equation 2 below.

Estimate=mod(P2/R2)×n×R1  (Equation 2)

Here, R1 is the resolution of the first position data detection circuit61. Moreover, mod is an operator that truncates the integer part andextracts only the fractional part. In Equation 2, the same symbols asused in Equation 1 represent the same physical quantities as those ofEquation 1.

The position data comparing and collating circuit 64 calculates a valueobtained by multiplying the value of the fractional part of thepositional ratio (P2/R2) within one rotation of the second position datadetection circuit 62 with the transmission ratio (n) and the resolutionR1 of the first position data detection circuit 61 as the estimate usingEquation 2.

In this case, since the value of the second position data P2 is 310, thevalue of the resolution R2 of the second position data detection circuit62 is 2048, the value of the transmission ratio n is 100, and the valueof the resolution R1 of the first position data detection circuit 61 is8192, the position data comparing and collating circuit 64 calculates1024 as the value of the estimate using Equation 2.

Subsequently, the position data comparing and collating circuit 64calculates an error estimate using Equation 3 below.

Error Estimate=Estimate−P1  (Equation 3).

Here, the estimate in Equation 3 is the estimate calculated by Equation2. The position data comparing and collating circuit 64 calculates adifference between the calculated estimate and the first position dataP1 as the error estimate using Equation 3. In this case, since the valueof the estimate is 1024, and the value of the first position data P1 is1000, the position data comparing and collating circuit 64 calculates 24as the value of the error estimate using Equation 3.

Subsequently, the position data comparing and collating circuit 64determines whether or not the absolute value of the error estimatecalculated by Equation 3 is equal to or smaller than, for example, 1/8of the resolution R1 of the first position data detection circuit 61. Inthis case, since the value of the calculated error estimate is 24, thevalue of the resolution R1 of the first position data detection circuit61 is 8192, and the absolute value of the calculated error estimate isequal to or smaller than 1/8 of the resolution R1 of the first positiondata detection circuit 61, the position data comparing and collatingcircuit 64 outputs normal as the determination result. If the absolutevalue of the calculated error estimate is not equal to or smaller than1/8 of the resolution R1 of the first position data detection circuit61, the position data comparing and collating circuit 64 outputsabnormal as the determination result.

As described above, in the encoder system of the present embodiment, itis assumed that the first encoder 3 which is an encoder of the inputshaft 10 is a so-called “single-rotation absolute encoder,” and isparticularly an optical encoder among many other types of encoders.

In addition, the encoder system uses the power transmission device 2having a predetermined transmission ratio and has the second encoder 4on the output shaft 11.

Here, the key point is that the second encoder 4 is a so-called magneticencoder, and the second encoder 4 is a single-rotation absolute encodersimilarly to the first encoder 3.

The feature of the present invention is that since both the firstencoder 3 and the second encoder 4 are single-rotation absoluteencoders, they do not require an external battery. Next, detaileddescription of how “multiple-rotation information” is obtained usingthese configurations will be provided.

Here, it is assumed that the transmission ratio of the powertransmission device 2 is 100. First, it should be noted that when theinput shaft 10 makes 100 rotations, the second encoder 4 rotates exactlyby 360°, namely makes one rotation. If the second encoder 4 is asingle-rotation absolute encoder which segments one rotation of theoutput shaft 11 into 100 segmented areas through interpolation and readthe segmented areas, by combining the data of both the first encoder 3and the second encoder 4 together, the encoder system can be configuredas a multiple-rotation absolute encoder capable of storing 100 rotationsof the multiple-rotation information of the input shaft 10.

By this principle, it is possible to realize an encoder system which hasmultiple-rotation information and which does not require an externalbattery.

Moreover, as described by way of an embodiment, the first encoder 3includes an interpolation circuit (for example, the second interpolationcircuit 621 of the signal processing circuit 6) and performs so-called“segmented reading.” That is, the pseudo-sinusoidal wave having a phasedifference of 90° is led from the second encoder 4 into the firstencoder 3 on the input shaft 10 side, and the interpolation circuitincluded in the first encoder 3 converts this signal into more finelysegmented position signals (namely, calculates the detailed position).

<Action>

Here, the signal obtained by the interpolation circuit can be treated assubstantially the same position information data as that of the firstencoder 3 depending on the resolution setting. That is, this encodersystem can be said to have a configuration in which there are two firstencoders 3. By comparing and collating these two systems of data, whenthere is a failure in any of the two systems regardless of which one ofthe first and second encoders 3 and 4 is the actual source of thefailure, it is possible to detect the failure using the comparing means.

This is what is called a dual or redundant detector system. That is, bymaking the detector system redundant, the reliability of the encodersystem can be improved.

Although the detector system is dual, one encoder is an optical encoder,and the other encoder is a magnetic encoder. The second encoder 4 whichis a magnetic encoder is cheaper than an optical encoder. Therefore,although the detector system is dual, the overall cost of the encodersystem is cheaper than that when two optical encoders are mounted.

From a different perspective, the present invention has a ground for theability to configure it advantageously for high robustness. That is itssuperior robustness to disturbances. Specifically, electromagnetic noisegenerally called electrical noise and disturbances can be roughlyclassified into one caused by an electric field and one caused by amagnetic field. For example, a magnetic encoder is vulnerable to amagnetic field disturbances, whereas the main cause of malfunction of anoptical encoder is an electric field as in general electronic circuits.

Although as for field disturbances, all sources of disturbances shouldbe taken into consideration, since the first encoder 3 described aboveis an optical encoder, it will not be affected even when it is exposedto magnetic noise. On the other hand, since the second encoder 4 is amagnetic encoder, it is a robust encoder which will not be affected byelectric field disturbances.

That is, it is possible to obtain a remarkable advantage in that thefirst encoder 3 and the second encoder 4 complement respective robustfeatures, thus constructing a robust encoder system.

In the description above, although the first encoder 3 has beendescribed to have the signal processing circuit 6 therein, the presentinvention is not limited to this. For example, the signal processingcircuit 6 may be provided in the second encoder 4, the powertransmission device 2, or the like. Moreover, the signal processingcircuit 6 may be configured as an independent device, and the encodersystem may have the signal processing circuit 6.

In the description above, although the output shaft 11 has beendescribed to be rotated by the input shaft 10 with its rotation speedreduced at the predetermined transmission ratio by the powertransmission device 2, the power transmission device 2 is not limited toone gear. For example, a power transmission device that rotates theinput shaft 10 by reducing the rotation speed of the output shaft 11 ata predetermined transmission ratio may be configured by one or pluralgears, belt devices, chain devices, and drive shaft devices or acombination of these gears and devices, and this power transmissiondevice may be used as the power transmission device 2. In this case,information representing the value of the transmission ratio of thepower transmission device is stored in the transmission ratioinformation storage section (transmission ratio information storagesection) 66 as the transmission ratio information.

It is assumed that the transmission ratio information storage section 66or the conversion table storage section 614 is configured by anonvolatile memory such as a hard disk device, an optomagnetic diskdevice, or a flash memory, a volatile memory such as a read-only storagemedium (for example, CD-ROM), or RAM (Random Access Memory), or acombination thereof.

The signal processing circuit 6 and the respective constituent circuitsof the signal processing circuit 6 shown in FIG. 3 may be realized byspecial-purpose hardware and may be realized by memories andmicroprocessors.

Moreover, the signal processing circuit 6 and the respective constituentcircuits of the signal processing circuit 6 may be realized byspecial-purpose hardware. Furthermore, the signal processing circuit 6and the respective constituent circuits of the signal processing circuit6 may be configured by memories and CPUs (Central Processing Unit), andprograms for realizing the functions of the signal processing circuit 6and the respective constituent circuits of the signal processing circuit6 may be loaded into the memories and executed, whereby the functionsare realized.

According to the present embodiment, it is possible to provide anencoder system and a signal processing method thereof, which does notrequire an external battery for storing absolute position informationand which extends the intervals of periodic maintenance to reduce aworkload for maintenance service.

Moreover, according to the present embodiment, it is possible to providea robust encoder system and a signal processing method thereof, which isnot greatly influenced under an environment with many disturbances andwhich is capable of preventing malfunctions that may stop an entireproduction line.

Furthermore, according to the present embodiment, it is possible toprovide an encoder system and a signal processing method thereof, whichis a multiple-rotation absolute encoder, which does not require anexternal battery for storing absolute position information, and which iscapable of improving the functional stability of the entire system.

In the present embodiment, the signal processing circuit of the encodersystem having the power transmission device that rotates the outputshaft at a predetermined transmission ratio in response to the rotationof the input shaft is configured to: detect the first position datarepresenting the positional displacement in the rotation of the inputshaft based on the first detection signal input from the first absoluteposition encoder; detect the second position data representing thepositional displacement in the rotation of the output shaft based on thesecond detection signal input from the second absolute position encoder;combine the first position data and the second position data to generatethe combined position data representing the number of rotations of theinput shaft and the positional displacement within one rotation of theinput shaft; and compare and collate the first position data and thesecond position data. Therefore, it is possible to provide an encodersystem and a signal processing method thereof, which is amultiple-rotation absolute encoder, which does not require an externalbattery for storing absolute position information, and which is capableof improving the functional stability of the entire system.

Next, another embodiment will be described. The same constituentelements as the above-described embodiment will be denoted by the samereference numerals, and description thereof will be omitted orsimplified.

In the present embodiment, as shown in FIG. 5, an encoder systemincludes a motor 1, a power transmission device 2, a first encoder(first absolute position encoder) 3, a second encoder (second absoluteposition encoder) 4, an input shaft 10, an output shaft 11, and acommunication line 12 for transmitting a signal representing themultiple-rotation count of the input shaft 10 from the second encoder tothe first encoder 3. Moreover, the encoder system includes a controller8 which is a high-order device, a communication line 9 which is acommunication line between the controller 8 and the first encoder 3, anda motor control line 14 for connecting the controller 8 and the motor 1.

The first encoder 3 and the second encoder 4 include, for example, arotating disc which has N and S poles and which rotates in response tothe rotation of a corresponding shaft among the input shaft 10 and theoutput shaft 11 and two Hall-effect elements as magnetic sensor deviceswhich are disposed at predetermined positions so that the mutual angleis at 90° with respect to the rotation center axis of the rotating disc.When the input shaft 10 or the output shaft 11 rotates, the rotatingdisc corresponding to the rotating shaft rotates as a rotary magnethaving the N and S poles, whereby a sinusoidal signal of which one cycle(one pulse period) corresponds to one rotation is output from theHall-effect elements. Since the Hall-effect elements are disposed so asto have a mutual angle of 90°, a sinusoidal wave having a phasedifference of 90°, namely a so-called biphasic pseudo-sinusoidal wave(for example, biphasic signals of A-phase and B-phase signals) is outputas the sinusoidal signal. The A-phase signal and the B-phase signal areshown in FIG. 7 as an example of the biphasic pseudo-sinusoidal wave.FIG. 7 will be described later.

For example, it is assumed that the resolution in one rotation of thesecond encoder 4 is M, and the power transmission device 2 connects theinput shaft 10 and the output shaft 11 at a ratio of 1:N. In this case,the second encoder 4 rotates by one digit whenever the first encoder 3makes one rotation. Therefore, it is possible to detect the rotationcount in the multiple rotations of the input shaft 10 based on theangular position of the second encoder 4 and to detect the positionaldisplacement in the rotation of the input shaft 10 based on the angularposition of the first encoder 3. Moreover, this encoder system iscapable of detecting N×M rotational positions, namely the absoluteposition in the rotation of the input shaft 10 until the output shaft 11makes one rotation.

In the present embodiment, the encoder system also functions as amultiple-rotation absolute encoder as the whole encoder system using thefirst encoder 3 which is a single-rotation absolute encoder and thesecond encoder 4 which is a single-rotation absolute encoder. Therefore,this encoder system does not require an external battery for storing theabsolute position information which was required in the encoder systemof the conventional art.

In the present embodiment, the encoder system includes a first signalprocessing circuit 6 and a second signal processing circuit 5 (secondposition data detection circuit 250 described later). For example, thefirst encoder 3 has the first signal processing circuit 6 therein.Moreover, the second encoder 4 has the second signal processing circuit5 therein.

The second signal processing circuit 5 receives the second detectionsignal detected by the second encoder 4. Moreover, the second signalprocessing circuit 5 detects second position data representing thepositional displacement in the rotation of the output shaft 11 throughpredetermined signal processing (second signal processing) based on thesecond detection signal input from the second encoder 4. That is, thesecond signal processing circuit 5 interpolates the second detectionsignal to detect the second position data.

Moreover, the second signal processing circuit 5 outputs the detectedsecond position data to the first encoder 3 through the communicationline 12. When detecting the second position data, the second signalprocessing circuit 5 detects the second position data at a predeterminedresolution that is, for example, at least twice of the transmissionratio of the power transmission device 2 as will be described later.

Moreover, the first encoder 3 has the first signal processing circuit 6therein. The first signal processing circuit 6 receives the secondposition data detected by the second encoder 4 through the communicationline 12. Moreover, the first signal processing circuit 6 interpolatesthe first detection signal detected by the first encoder 3 to detectfirst position data representing the angular position of the input shaft10.

Moreover, the first signal processing circuit 6 detects combinedposition data representing the rotation count of the input shaft 10 andthe positional displacement within one rotation of the input shaft 10based on the detected first position data and the input second positiondata. Then, the first signal processing circuit 6 outputs the detectedcombined position data to the controller 8 through the communicationline 9.

In this way, the controller 8 is able to detect the rotation count ofthe input shaft and the positional displacement within one rotation ofthe input shaft 10 based on the combined position data from the encodersystem serving as the multiple-rotation absolute encoder. Moreover, thecontroller 8 controls the rotation of the motor 1 through the motorcontrol line 14 based on the input combined position data.

The first signal processing circuit 6 and the second signal processingcircuit 5 are connected by a setting control line 13. The first signalprocessing circuit 6 changes the setting values stored in a storagesection, described later, included in the second signal processingcircuit 5 through the setting control line 13.

Next, the configuration of the encoder system described using FIG. 5,particularly the configuration of the first and second signal processingcircuits 6 and 5 will be described using FIG. 6. In FIG. 6, the sameconstituent elements as those in FIG. 5 will be denoted by the samereference numerals, and description thereof will be omitted.

<Configuration of First and Second Signal Processing Circuits 6 and 5>

The second signal processing circuit 5 includes a second position datadetection circuit 250. The second position data detection circuit 250includes a second interpolation circuit (interpolation circuit) 251, asecond position detection circuit (position detection circuit) 252, atransmission signal generation and output section 253, a transmissionratio information storage section 256, a first resolution storagesection 257, a second resolution storage section 258, and a conversioninformation storage section 259. On the other hand, the first signalprocessing circuit 6 includes a first position data detection circuit261, a second position data correction circuit 262, a position datacombination circuit 263, a rotation count storage section 264, anexternal communication circuit 265, a transmission ratio informationstorage section 266, a first resolution storage section 267, and asecond resolution storage section 268.

<Respective Configurations of Second Position Data Detection Circuit250>

First, the respective configurations of the second position datadetection circuit 250 will be described. In the transmission ratioinformation storage section 256, information representing the value of apredetermined transmission ratio (for example, a gear ratio) of thepower transmission device 2 connecting the first encoder 3 and thesecond encoder 4 is stored in advance as transmission ratio information.In the first resolution storage section 257, the resolution of the firstposition data detection circuit 261 is stored in advance as a firstresolution. In the second resolution storage section 258, the resolutionof the second position data detection circuit 250 is stored in advanceas a second resolution.

The second interpolation circuit 251 interpolates the second detectionsignal input from the second encoder 4 to detect the second positiondata. The second position detection circuit 252 calculates a value ofthe integer part of a value obtained by dividing a value which isobtained by multiplying the second position data detected by the secondinterpolation circuit 251 and the transmission ratio information readout from the transmission ratio information storage section 256 by thevalue of the second resolution read out from the second resolutionstorage section 258 as the rotation count and calculates a valueobtained by multiplying a value of the fractional part of the dividedvalue and the value of the first resolution read out from the firstresolution storage section 257 as the estimate. This estimate is theestimated position data of the accurate first position data detected bythe first encoder 3, calculated based on the second detection signaldetected by the second encoder 4.

For example, the second position detection circuit 252 calculates therotation count (m) and the estimate using Equations 4 and 5 below.

Rotation Count (m)=INT(n(P2/R2))  (Equation 4)

Estimate=n(P2/R2)−m  (Equation 5)

In Equations 4 and 5, P2 is the second position data detected by thesecond interpolation circuit 251, R2 is the second resolution stored inthe second resolution storage section 258, and n is the transmissionratio information read out from the transmission ratio informationstorage section 256. Moreover, INT is an operator that truncates thefractional part and extracts only the integer part.

In this way, the second position data detection circuit 250 calculatesthe rotation count of the first encoder 3 and calculates the positiondata corresponding to the first position data as the estimate based onthe interpolated value of the second detection signal detected by thesecond encoder 4 and the transmission ratio information read out fromthe transmission ratio information storage section 256 by using thesecond interpolation circuit 251 and the second position detectioncircuit 252.

The second position data detection circuit 250 will be described infurther detail. In the conversion information storage section 259, thesecond detection signal and the second position data are stored inadvance in a correlated manner. In addition, in the conversioninformation storage section 259, when the value of the first signal ofthe biphasic sinusoidal signal is larger than that of the second signal,the value obtained by dividing the second signal by the first signal andthe second position data corresponding to the divided value are storedin advance, and when the value of the first signal is smaller than thatof the second signal, the value obtained by dividing the first signal bythe second signal and the second position data corresponding to thedivided value are stored in advance.

The second interpolation circuit 251 reads out second position datacorresponding to the second detection signal output by the secondencoder 4 from the conversion information storage section 259 to detectthe second position data. When the value of the first signal of thebiphasic sinusoidal signal is larger than that of the second signal, thesecond interpolation circuit 251 detects the second position data byreading out the second position data corresponding to a value obtainedby dividing the second signal by the first signal from the conversioninformation storage section 259. On the other hand, when the value ofthe first signal of the biphasic sinusoidal signal is smaller than thatof the second signal, the second interpolation circuit 251 detects thesecond position data by reading out the second position datacorresponding to a value obtained by dividing the first signal by thesecond signal from the conversion information storage section 259.

Here, the second detection signal and the second position data stored inadvance in the conversion information storage section 259 in acorrelated manner will be described using FIG. 7. In this description,it is assumed that the second detection signal is a biphasic sinusoidalsignal, the first signal of the biphasic sinusoidal signal is an A-phasesignal, and the other of the biphasic sinusoidal signal is a B-phasesignal. In FIG. 7, the horizontal axis x corresponds to the phase 0 to2π (in the drawing, −π to π) in one rotation of the output shaft 11,namely the second position data. Moreover, the vertical axis ycorresponds to a curve C for detecting the second position data from theA-phase signal, the B-phase signal, and the second detection signal.

Here, the A-phase signal and the B-phase signal are sinusoidal wavesoutput from the Hall-effect elements, and since the Hall-effect elementsare disposed so as to have the mutual angle of 90° in the secondencoder, the phases thereof are different by 90°. Therefore, the A-phasesignal and the B-phase signal have the relationship of SIN and COS, forexample. In this example, the A-phase signal is described as SIN, andthe B-phase signal is described as COS (in the drawing, -COS).

When the value of the A-phase signal is larger than the value of theB-phase signal, a value obtained by dividing the value of the B-phasesignal by the value of the A-phase signal, namely the value of COT whichis a division of COS by SIN corresponds to the value of the curve C.Conversely, when the value of the A-phase signal is smaller than thevalue of the B-phase signal, a value obtained by dividing the value ofthe A-phase signal by the value of the B-phase signal, namely the valueof TAN which is a division of SIN by COS corresponds to the value of thecurve C. In the conversion information storage section 259, the COT orTAN corresponding to the second detection signal and the second positiondata are stored in a correlated manner using the value of the curve C.

Upon receiving the second detection signal, namely the value of theA-phase signal and the value of the B-phase signal of the biphasicsinusoidal signal from the second encoder 4, first, the secondinterpolation circuit 251 determines which one of the value of theA-phase signal and the value of the B-phase signal is the larger. Whenit is determined that the value of the A-phase signal is larger than thevalue of the B-phase signal, the second interpolation circuit 251divides the value of the B-phase signal by the value of the A-phasesignal and reads out second position data corresponding to the dividedvalue from the conversion information storage section 259 to detect thesecond position data. Conversely, when it is determined that the valueof the A-phase signal is smaller than the value of the B-phase signal,the second interpolation circuit 251 divides the value of the A-phasesignal by the value of the B-phase signal and reads out second positiondata corresponding to the divided value from the conversion informationstorage section 259 to detect the second position data.

The use of the conversion information storage section 259 and the secondinterpolation circuit 251 provides the following advantageous effects.First, there is a possibility that any one of the A-phase signal and theB-phase signal has a value close to 0 depending on the phases thereof.In this case, if the second signal is divided by the first signal havingthe value close to 0, since the calculated value may diverge, there is apossibility that it is unable to perform calculation properly. Moreover,even if the calculation was possible, there is a possibility that thecalculation error increases.

Here, the A-phase signal and the B-phase signal of the biphasicsinusoidal signal have different phases and have the relationship of COSand SIN, for example. Therefore, the A-phase signal and the B-phasesignal will not have values close to 0 at the same time. Accordingly,even when the first signal has a value close to 0, by dividing thesecond signal by the first signal having the larger value as describedabove, the division can be properly calculated. Moreover, since thedivision is computed using a divisor having a larger value than 0, thereis no possibility that the division error increases. By doing so, thedivision can be properly computed, and the second interpolation circuit251 can properly detect the second position data from the seconddetection signal with a reduced error.

In this way, in the present embodiment, it is possible to convert twopieces of signal information, namely the value of the A-phase signal andthe value of the B-phase signal into one piece of signal information,namely the value obtained by dividing the first signal by the secondsignal and to detect the second position data based on one piece ofsignal information.

In each predetermined phase interval in one rotation of the outputshaft, the second detection signal and the second position data are in arelationship such that they are identical or a relationship such thatthey are mirror-symmetrical about a line corresponding to the centralphase of the phase interval. For example, in FIG. 7, there are foursymmetrical phase intervals: that is, a first phase interval of from −πto −(3/4)π and from (3/4)π to π; a second phase interval of from −(3/4)πto −(1/4)π; a third phase interval of from −(1/4)π to (1/4)π; and afourth phase interval of from (1/4)π to (3/4)π. Moreover, looking at thephase interval of the first and third phase intervals and the phaseinterval of the second and fourth phase intervals, the second detectionsignal and the second position data are in a relationship such that theyare identical. Moreover, looking at the first and second phaseintervals, the second detection signal and the second displacement inthe first position data are in a relationship such that they areidentical to the second detection signal and the second position data inthe second phase interval which are mirror-symmetrical about the centralphase of the second phase interval, namely −(1/2)π.

As described above, since the second detection signal and the secondposition data in each phase interval are in a relationship such thatthey are identical or a relationship such that they aremirror-symmetrical, the conversion information storage section 259 isable to store the second detection signal and the second position datafor only one phase interval in advance in a correlated manner. Forexample, as shown in FIG. 8, the second detection signal and the secondposition data for only one phase interval, namely in the third phaseinterval of from −(1/4)π to (1/4)π are stored in advance in a correlatedmanner. By doing so, the data quantity of the second detection signaland the second position data which need to be stored in advance in theconversion information storage section 259 can be decreased.

Moreover, in this case, first, the second interpolation circuit 251determines which phase interval the rotational position of the outputshaft corresponds to, among a plurality of phase intervals correspondingto one rotation of the output shaft. Then, the second interpolationcircuit 251 calculates the second position data in one rotation of therotation of the output shaft based on a predetermined reference phasecorresponding to the determined phase interval and the second positiondata in one phase interval read out from the conversion informationstorage section 259 to detect the second position data. For example, thesecond interpolation circuit 251 adds the value of the reference phaseand the value of the second position data to detect the second positiondata.

For example, the second interpolation circuit 251 determines which of aplurality of conditions determined in advance based on the value of thesecond detection signal, the input value of the second detection signalsatisfies. Then, the second interpolation circuit 251 selects a phaseinterval correlated in advance to the satisfied condition, thusdetermining which phase interval, the rotational position of the outputshaft corresponds to, among a plurality of phase intervals correspondingto one rotation of the output shaft.

For example, in FIG. 7, the plurality of conditions determined inadvance based on the value of the second detection signal and the phaseintervals correlated to the conditions have the following relationships.

(1) The first phase interval is selected when the value of the A-phasesignal is smaller than the value of the B-phase signal ([A-phase signalvalue]<[B-phase signal value]) and the value of the B-phase signal ispositive ([B-phase signal value]>0).

(2) The second phase interval is selected when the value of the A-phasesignal is larger than the value of the B-phase signal ([A-phase signalvalue]>[B-phase signal value]) and the value of the A-phase signal isnegative ([A-phase signal value]<0).

(3) The third phase interval is selected when the value of the A-phasesignal is smaller than the value of the B-phase signal ([A-phase signalvalue]<[B-phase signal value]) and the value of the B-phase signal isnegative ([B-phase signal value]<0).

(4) The fourth phase interval is selected when the value of the A-phasesignal is larger than the value of the B-phase signal ([A-phase signalvalue]>[B-phase signal value]) and the value of the A-phase signal ispositive ([A-phase signal value]<0).

For these respective phase intervals, reference phases are determined inadvance. For example, the value of the central phase of each phaseinterval is determined in advance as the reference phase. For example,the value of the reference phase of the first phase interval is −π (orπ), the value of the reference phase of the second phase interval is−(1/2)π, the value of the reference phase of the third phase interval is0, and the value of the reference phase of the fourth phase interval is(1/2)π.

The reference phases may be stored in advance in a reference phasestorage section of the second position data detection circuit 250 so asto be correlated to the respective phase intervals, for example. In thiscase, as described above, the second interpolation circuit 251 selectsthe phase interval and reads out a reference phase corresponding to theselected phase interval from the reference phase storage section. Inaddition, the second interpolation circuit 251 divides the value of oneof the A-phase signal and the B-phase signal of the biphasic sinusoidalsignal by the value of the other one having the larger value and readsout the second position data corresponding to the divided value from theconversion information storage section 259 based on the symmetricalproperty of the selected phase interval. Then, the second interpolationcircuit 251 adds and combines the read second position data and the readreference phase to detect the second position data.

In the description above, although the phase is divided into the fourphase intervals of the first to fourth phase intervals, the phasedividing method is not limited to this. For example, as shown in FIG. 8,the second detection signal and the second position data in the intervalfrom −(1/4)π to (1/4)π are point-symmetrical about the origin 0.Therefore, if only the information for the interval from 0 to (1/4)π isgiven, it is possible to calculate the information for the interval from−(1/4)π to 0 from the point symmetrical property. Accordingly, thesecond detection signal and the second position data which need to bestored in advance in the conversion information storage section 259 maybe the information for the interval from 0 to (1/4)π, and the dataquantity thereof can be further decreased.

<Respective Configurations of First Signal Processing Circuit 6>

Next, the respective configurations of the first signal processingcircuit 6 shown in FIG. 6 will be described. In the transmission ratioinformation storage section 266, similarly to the transmission ratioinformation storage section 256, information representing the value of apredetermined transmission ratio (for example, a gear ratio) of thepower transmission device 2 connecting the first encoder 3 and thesecond encoder 4 is stored in advance as transmission ratio information.In the first resolution storage section 267, similarly to the firstresolution storage section 257, the resolution of the first positiondata detection circuit 261 is stored in advance as a first resolution.In the second resolution storage section 268, similarly to the secondresolution storage section 258, the resolution of the second positiondata detection circuit 250 is stored in advance as a second resolution.

The first position data detection circuit 261 detects first positiondata representing the angular position of the input shaft 10 throughfirst predetermined signal processing based on the first detectionsignal input from the first encoder 3.

The second position data correction circuit 262 corrects the secondposition data detected by the second position data detection circuit 250through predetermined correction processing based on the second positiondata and the first position data detected by the first position datadetection circuit 261.

The position data combination circuit 263 combines the first positiondata detected by the first position data detection circuit 261 and thesecond position data corrected by the second position data correctioncircuit 262 to generate combined position data representing the rotationcount of the input shaft and the positional displacement within onerotation of the input shaft.

Next, the configuration of the second position data correction circuit262 and the position data combination circuit 263 will be described infurther detail. The second position data correction circuit 262 correctsthe second position data detected by the second position data detectioncircuit 250 through predetermined correction processing based on thevalue of the second position data and the value of the first positiondata detected by the first position data detection circuit 261.

That is, when the value of the estimate calculated by the secondposition detection circuit 252 is equal to or larger than a firstpredetermined reference value, and the value of the first position datadetected by the first position data detection circuit 261 is smallerthan a second predetermined reference value, the second position datacorrection circuit 262 corrects the rotation count of the first encoder3 by adding 1 to the value of the integer part of the rotation count.Moreover, when the value of the estimate calculated by the secondposition detection circuit 252 is smaller than a third predeterminedreference value equal to or smaller than the first reference value, andthe value of the first position data detected by the first position datadetection circuit 261 is equal to or larger than a fourth predeterminedreference value equal to or larger than the second reference value, thesecond position data correction circuit 262 corrects the rotation countof the first encoder 3 by subtracting 1 from the value of the integerpart of the rotation count.

The predetermined first, second, third, and fourth reference valuesdescribed above will be described using FIGS. 9 and 10.

Next, a rotation count correction method by the second position datacorrection circuit 262 will be described using FIGS. 9 and 10. In thisexample, a case in which the value of the first position data is 17 bitwill be described.

As shown in FIG. 9, the output shaft 11 rotates with the rotation of theinput shaft 10, and the rotation count m is calculated based on thevalue P2 of the second position data. Moreover, the value P1 of thefirst position data repeats the values from 0 to 131071 (=2¹⁷−1). Thatis, when the value P1 of the first position data repeats the values from0 to 131071 (=2¹⁷−1), the rotation count m changes in the order of 10,11, 12. There is a shift between the position of change (for example,the time when the value P1 of the first position data becomes 0) in theinput shaft rotation count detected based on the value P1 of the firstposition data and the time when the rotation count m changes.

As shown in FIG. 10, for example, when the value P1 of the firstposition data is within the range of 0 to 32767 (=2¹⁷×1/4−1), and thecalculated rotation count m is in the posterior half region, the secondposition data correction circuit 262 corrects the value of the rotationcount m by adding a correction value Δm (=1) to the value of therotation count m. Here, the calculated rotation count m being in theposterior half region means that the value of the calculated rotationcount m is actually m but is close to m+1.

Moreover, as shown in FIG. 10, for example, when the value P1 of thefirst position data is within the range of 98304 (=2¹⁷×3/4−1) to 131071(=2¹⁷−1), and the calculated rotation count m is in the anterior halfregion, the second position data correction circuit 262 corrects thevalue of the rotation count m by adding a correction value Δm (=−1) tothe value of the rotation count m. Here, the calculated rotation count mbeing in the anterior half region means that the value of the calculatedrotation count m is actually m but is close to m−1.

The determination as to whether the calculated rotation count m is inthe posterior half region or the anterior half region is made based onthe value of the estimate. For example, when the value of the estimatecalculated by the second position detection circuit 252 is smaller than0.5 (half cycle), the second position data correction circuit 262determines that the rotation count in is in the anterior half region.When the value of the estimate is equal to or larger than 0.5 (halfcycle), the rotation count m is determined to be in the posterior halfregion.

In this case, the first and third reference values are 0.5, the secondreference value is 32767 (=2¹⁷×1/4−1), and the fourth reference value is98304 (=2¹⁷×3/4−1). That is, the second reference value is 1/4 of thevalue of the first resolution read out from the first resolution storagesection 267. Moreover, the fourth reference value is 3/4 of the value ofthe first resolution read out from the first resolution storage section267.

The first and third reference values are reference values for detectingwhether the rotational position of the input shaft 10 estimated based onthe value of the estimate calculated by the second position detectioncircuit 252 is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region. Moreover,the second and fourth reference values are reference values fordetecting whether the rotational position of the input shaft 10 detectedbased on the value of the rotation count detected by the first encoder 3is in the posterior half region (in this case, the starting 1/4 regionof one rotation) of the rotation in one rotation of the input shaft 10or the posterior half region (in this case, the ending 1/4 region of onerotation).

In this way, the second position data correction circuit 262 determineswhether the rotational position of the input shaft 10 estimated based onthe value of the estimate calculated by the second position detectioncircuit 252 is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region anddetermines whether the rotational position of the input shaft 10detected based on the value of the rotation count detected by the firstencoder 3 is in the anterior half region of the rotation in one rotationof the input shaft 10 or the posterior half region. Moreover, when thetwo determination results are different, the second position datacorrection circuit 262 corrects the value of the rotation countcalculated by the second position detection circuit 252.

Specifically, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 252 is in the posterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 261is in the anterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 262 correctsthe value of the rotation count calculated by the second positiondetection circuit 252 by adding 1 to the value of the rotation count.

On the other hand, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 252 is in the anterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 261is in the posterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 262 correctsthe value of the rotation count calculated by the second positiondetection circuit 252 by adding −1 to the value of the rotation count,namely by subtracting 1 from the value of the rotation count.

For the second position data correction circuit 262 to correct the valueof the rotation count calculated by the second position detectioncircuit 252, it is necessary to determine whether the rotationalposition of the input shaft 10 estimated based on the value of theestimate calculated by the second position detection circuit 252 is inthe anterior half region of the rotation in one rotation of the inputshaft 10 or the posterior half region. That is, the second positiondetection circuit 252 needs to detect the second position data at apredetermined resolution that is, for example, at least twice of thetransmission ratio of the power transmission device 2. Therefore, thesecond position detection circuit 252 needs to output the rotation countto the second position data correction circuit 262 so that it candetermine whether or not the rotational position is in the anterior halfregion of the rotation in one rotation of the input shaft 10 or theposterior half region. This transmission method will be described inconjunction with the transmission signal generation and output section253 described later.

The position data combination circuit 263 generates combined positiondata based on the value of the rotation count of the first encoder 3corrected by the second position data correction circuit 262 and thevalue of the first position data detected by the first position datadetection circuit 261. When combining the first position data detectedby the first position data detection circuit 261 and the second positiondata detected by the second position data detection circuit 250, theposition data combination circuit 263 generates the combined positiondata based on the transmission ratio information read out from thetransmission ratio information storage section 266.

Moreover, specifically, when combining the first position data detectedby the first position data detection circuit 261 and the second positiondata detected by the second position data detection circuit 250, theposition data combination circuit 263 generates the combined positiondata by a predetermined calculation method based on the transmissionratio information read out from the transmission ratio informationstorage section 266, the first resolution read out from the firstresolution storage section 267, and the second resolution read out fromthe second resolution storage section 268.

The position data combination circuit 263 outputs the combined positiondata generated by the position data combination circuit 263 to thecontroller 8 through the communication line 9 using the externalcommunication circuit 265.

Moreover, the external communication circuit 265 executes processing forcommunication with the controller 8 through the communication line 9.For example, the external communication circuit 265 stores thetransmission ratio information received from the controller 8 throughthe communication line 9 in the transmission ratio information storagesection 266 and stores the transmission ratio information to thetransmission ratio information storage section 256 through the settingcontrol line 13.

Moreover, the external communication circuit 265 stores the firstresolution received from the controller 8 through the communication line9 in the first resolution storage section 267 and stores the firstresolution in the first resolution storage section 257 through thesetting control line 13. Furthermore, the external communication circuit265 stores the second resolution received from the controller 8 throughthe communication line 9 in the second resolution storage section 268and stores the second resolution in the second resolution storagesection 258 through the setting control line 13.

The transmission ratio information storage sections 266 and 256 arenonvolatile memories, for example. Therefore, once the value of thetransmission ratio information stored in the transmission ratioinformation storage section 266 is set, it will not be erased even whenthe encoder system is powered off. According to this configuration, itis possible to broaden the choices for the power transmission device 2and the transmission ratio of the power transmission device 2 usable inthe encoder system.

Moreover, the first resolution storage sections 257 and 267 and thesecond resolution storage sections 258 and 268 are also nonvolatilememories, for example, similarly to the transmission ratio informationstorage sections 266 and 256. Therefore, it is possible to broaden thechoices for the power transmission device 2 and the transmission ratioof the power transmission device 2 usable in the encoder system.

Next, the transmission signal generation and output section 253 of thesecond position data detection circuit 250 will be described using FIG.11. The transmission signal generation and output section 253 generatesa transmission signal representing the value of the rotation count andwhether the rotational position of the input shaft corresponding to therotation count is in the anterior half region of the rotation in onerotation of the input shaft or the posterior half region based on theestimate calculated by the second position detection circuit 252 andoutputs the transmission signal to the second position data correctioncircuit 262. For example, the transmission signal generation and outputsection 253 of the second position data detection circuit 250 generatesthe transmission signal representing whether or not the value of thecalculated estimate is equal to or smaller than the first referencevalue and whether or not the value of the calculated estimate is smallerthan the third reference value based on the calculated estimate andoutputs the generated transmission signal to the second position datacorrection circuit 262.

The transmission signal generation and output section 253 generates andoutputs multiple-rotation A and B signals which are first and secondrectangular signals of which the phases are different by 90°, forexample, as the transmission signal (see FIG. 11).

In FIG. 11, when the input shaft makes one rotation, namely when thefirst position data assumes the values from 0 to 131071, themultiple-rotation A signal and the multiple-rotation B signal change inthe signal pattern of H and L; H and H; L and H, and L and L. Here, Hand L are the potentials of an electrical signal and are, for example,high and low levels, respectively. Moreover, whenever the input shaftmakes one rotation, the multiple-rotation A signal and themultiple-rotation B signal repeat the above-described signal pattern.

The multiple-rotation A and B signals generated by the transmissionsignal generation and output section 253 have the following reliabilityin accordance with the transmission ratio n and the resolution R2 of thesecond position data detection circuit 250 in one rotation of the inputshaft.

The multiple-rotation A signal is H in a period where the residue ofR2/4n is 0 to 2n and is L in the other periods. On the other hand, themultiple-rotation B signal is H in a period where the residue of R2/4nis n to 3n and is L in the other periods.

For example, the transmission signal generation and output section 253generates the above-described multiple-rotation A and B signals in thefollowing manner. The transmission signal generation and output section253 outputs H for the multiple-rotation A signal when a value obtainedby subtracting 4n from a value obtained by multiplying the resolution R2of the second position data detection circuit 250 with the estimatecalculated by the second position detection circuit 252 is within therange of 0 to 2n, and outputs L for the multiple-rotation A signal whenthe value is outside the range. Moreover, the transmission signalgeneration and output section 253 outputs H for the multiple-rotation Bsignal when a value obtained by subtracting 4n from a value obtained bymultiplying the resolution R2 of the second position data detectioncircuit 250 with the estimate calculated by the second positiondetection circuit 252 is within the range of 1n to 3n, and outputs L forthe multiple-rotation B signal when the value is outside the range.

In this way, the transmission signal generation and output section 253generates and outputs the transmission signal corresponding to therotation of the input shaft 10 based on the second position datadetected by the second position data detection circuit 250. Thetransmission signal generation and output section 253 generates aplurality of signals, of which one cycle corresponds to one rotation ofthe input shaft 10, and of which the phases are different, as thetransmission signal.

The transmission signal is a biphasic rectangular wave of which onecycle corresponds to one rotation of the input shaft 10.

Moreover, in this way, the transmission signal generation and outputsection 253 generates and outputs the transmission signal based on theestimate (the residue of R2/4n) calculated by the second position datadetection circuit 250. Moreover, since the estimate is based on thetransmission ratio information, the transmission signal is based on thetransmission ratio information. That is, the transmission signalgeneration and output section 253 generates and outputs the transmissionsignal based on the transmission ratio information.

Therefore, even when the transmission ratio of the power transmissiondevice is changed, by changing the value of the transmission ratioinformation stored in the transmission ratio information storage section256, the transmission signal generation and output section 253 is ableto generate and output the transmission signal described above.Accordingly, the encoder system can use a power transmission devicehaving an arbitrary transmission ratio.

Then, the second position data correction circuit 262 determines whetherthe rotational position of the input shaft corresponding to the rotationcount is in the anterior half region of the rotation in one rotation ofthe input shaft or the posterior half region based on the transmissionsignal input from the transmission signal generation and output section253 of the second position data detection circuit 250 and corrects thevalue of the rotation count. For example, the second position datacorrection circuit 262 determines whether or not the value of thecalculated estimate is equal to or smaller than the first referencevalue and whether or not the value of the calculated estimate is smallerthan the third reference value based on the transmission signal inputfrom the transmission signal generation and output section 253 of thesecond position data detection circuit 250 and corrects the value of therotation count.

For example, the multiple-rotation A and B signals change in the signalpattern of H and L; H and H; L and H; and L and L whenever the inputshaft makes one rotation, Therefore, when the multiple-rotation A and Bsignals are H and L, or H and H, respectively, the second position datacorrection circuit 262 determines that the rotational position is in theanterior half region of the rotation in one rotation of the input shaft.On the other hand, when the multiple-rotation A and B signals are L andH, or L and L, respectively, the second position data correction circuit262 determines that the rotational position is in the posterior halfregion of the rotation in one rotation of the input shaft.

More specifically, when the multiple-rotation A and B signals are H andL, respectively, the second position data correction circuit 262determines that the rotational position is in the starting 1/4 region ofthe rotation in one rotation of the input shaft. Moreover, when themultiple-rotation A and B signals are L and L, respectively, the secondposition data correction circuit 262 determines that the rotationalposition is in the ending 1/4 region of the rotation in one rotation ofthe input shaft.

Moreover, the second position data correction circuit 262 detects thatthe input shaft has made one rotation by detecting that the inputmultiple-rotation A and B signals have changed sequentially in thesignal pattern of H and L; H and H; L and H; and L and L. On the otherhand, the second position data correction circuit 262 detects that theinput shaft has made one rotation in a reverse direction, namely −1rotation, by detecting that the input multiple-rotation A and B signalshave changed sequentially in the signal pattern of L and L; L and H; Hand H; and H and L.

That is, the second position data correction circuit 262 receives thetransmission signal as the plurality of signals, detects an increment ora decrement of the number of rotations of the input shaft 10 based on acombination of the plurality of received signals, and adds the detectedincrement or decrement of the number of rotations to the value of therotation count of the input shaft 10 read out from the rotation countstorage section 264, thus calculating the rotation count of the inputshaft 10.

<Setting Method During Startup>

The transmission signal described above enables transmission of theinterference fringe representing that the value of the rotation counthas increased by 1 or the value of the rotation count has decreased by1, from the second signal processing circuit 5 to the first signalprocessing circuit 6, but it is not possible to transmit the value ofthe rotation count itself. Therefore, when the encoder system is poweredON, the initial value of the rotation count is output from the secondsignal processing circuit 5 to the first signal processing circuit 6,and the initial value is stored in the first signal processing circuit6. After that, the first signal processing circuit 6 increases ordecreases the initial value by 1 in response to reception of thetransmission signal from the second signal processing circuit 5, thusdetecting the value of the rotation count.

For example, when the encoder system is powered ON, the transmissionsignal generation and output section 253 of the second signal processingcircuit 5 outputs a multiple-rotation signal which repeats the signalpattern of the above-described multiple-rotation A and B signals at acycle of 1 KHz as an initial value setting signal. Moreover, thetransmission signal generation and output section 253 of the secondsignal processing circuit 5 outputs a signal corresponding to the valueof the second position data detected by the second position datadetection circuit 250 and then stops this outputting. That is, thetransmission signal generation and output section 253 of the secondsignal processing circuit 5 outputs the initial value setting signal asthe pulse count of the multiple-rotation signal corresponding to thevalue of the second position data (see FIG. 12). For example, FIG. 12shows the multiple-rotation signal output by the transmission signalgeneration and output section 253 when the value of the rotation countis as shown in FIG. 11.

Moreover, the second position data correction circuit 262 stores a valuecorresponding to the initial value setting signal received from thetransmission signal generation and output section 253 of the secondsignal processing circuit 5 in the rotation count storage section 264.As a result, the rotation count information is set in the first signalprocessing circuit 6.

As described above, in order to set the rotation count information inthe rotation count storage section 264 at the time of power-ON, forexample, the second signal processing circuit 5 has a transmission-sideinitialization setting section that generates and outputs thetransmission signal for cycles corresponding to the rotation count ofthe input shaft 10 based on the second position data detected by thesecond position data detection circuit 250 when power is on. Moreover,the first signal processing circuit 6 has a reception-sideinitialization setting section that stores the value of the rotationcount of the input shaft 10 measured based on the received transmissionsignal for the cycles in the rotation count storage section 264 uponreceiving the transmission signal for cycles corresponding to therotation count of the input shaft 10 from the transmission-sideinitialization setting section.

The transmission-side initialization setting section may be included inthe transmission signal generation and output section 253 and may beintegrated with the transmission signal generation and output section253. Moreover, the reception-side initialization setting section may beincluded in the second position data correction circuit 262 or theposition data combination circuit 263 and may be integrated with thesecond position data correction circuit 262 or the position datacombination circuit 263.

After that, the second position data correction circuit 262 detects thevalue of the rotation count by increasing or decreasing the value of therotation count stored in the rotation count storage section 264 by 1 inresponse to reception of the transmission signal from the second signalprocessing circuit 5.

<When Transmission Signal is Serial Signal>

For example, in order for the second signal processing circuit 5 totransmit the position of 10 rotations at a resolution, for example, of8n (8 times of the transmission ratio), specifically, a resolution of800 using 100 as the value of n, it is necessary to transmit a value of80 to the first signal processing circuit 6.

If the transmission signal is a serial signal, when the power is ON, aposition data transmission request signal is transmitted from the firstsignal processing circuit 6 to the second signal processing circuit 5 as8-bit serial data and 3-bit CRC data. Here, CRC is an abbreviation ofCyclic Redundancy Check, and when it is appended to transmission data,the receiver side is able to recognize the presence of an error in theserial data using the CRC bit.

If there is no error, upon receiving the position data transmissionrequest signal, the second signal processing circuit 5 transmits 16-bitposition information of the second encoder 4 and 8-bit CRC data to thefirst signal processing circuit 6 at three different times. Transmittingthe same data at three different times is to ensure the reliability ofdata. At that time, if the data transmitted at three different times arenot identical, the first signal processing circuit 6 transmitsinformation indicative of an error to the controller 8. In this way, thecontroller 8 can detect an error in the initialization.

In the case of a serial signal, the transmission signal generation andoutput section 253 generates and outputs serial data corresponding tothe number of rotations of the input shaft 10 as the transmissionsignal.

<Compatibility with Conventional Transmission Method>

The conventional multiple-rotation absolute encoder performswaveform-shaping of the signal from a magnetic sensor such as aHall-effect element to generate signals like the multiple-rotation A andB signals shown in FIG. 11. Then, a signal processing device generatesoutput data based on the generated signals while ensuring consistencywith one-rotation data of the motor shaft.

In the present embodiment, the second signal processing circuit 5generates the above-described transmission signal (multiple-rotation Aand B signals) and outputs the transmission signal to a signalprocessing device, namely the first signal processing circuit 6similarly to the multiple-rotation signal of the conventionalmultiple-rotation absolute encoder. Therefore, the first signalprocessing circuit 6 receives the same signal as that of theconventional signal processing device.

As a result, according to the present embodiment, although no battery isused, the first signal processing circuit 6 can handle the transmissionsignal, namely the multiple-rotation A and B signals which aremultiple-rotation signals in the same manner as the conventionalmultiple-rotation absolute encoder. However, the processing of thetransmission signal, detection of the rotation count, correctionprocessing, and the like are performed differently in the internalsections of the first signal processing circuit 6.

Moreover, although the transmission signal generation and output section253 may output the output signal as an analog signal, in the presentembodiment, as described above, the output signal is output as thebiphasic rectangular wave, namely the multiple-rotation A and B signals.Analog signals are weak to disturbance noise, and the cost forcountermeasures against noise may increase if the encoder system isoperated in a real situation. Contrary to the analog signal, in thepresent embodiment, since the output signal is output as the biphasicrectangular wave as described above, the output signal is robust todisturbance noise and does not increase the cost.

Moreover, as described above, when data are transmitted from the secondencoder to the first encoder by a serial communication method, similarlyto the biphasic rectangular wave, the reliability of its noiseresistance level is high. However, in the case of the serialcommunication method, the second encoder needs to have a circuit forconverting the position data into serial data and a decoding circuit forenabling the first encoder to process the serial data from the secondencoder, and this may increase a cost. In contrast, since the outputsignal is output as the biphasic rectangular wave, the circuit forconverting to the serial data and the decoding circuit are not required,and it is possible to suppress the increase of costs.

As described above, in the present embodiment, by using the biphasicrectangular wave, it is possible to suppress the increase of costswithout decreasing the noise resistance of the communication method usedfor transmitting data from the second encoder to the first encoder.

In the conventional encoder, a signal representing information onrotation was output from a device corresponding to the second detectionsection to a device corresponding to the first detection section as thebiphasic rectangular wave. However, the biphasic rectangular wave is asignal of which one cycle corresponds to one rotation of the outputshaft.

According to the present embodiment, as described above, although thebiphasic rectangular wave is output from the second detection section tothe first detection section, the biphasic rectangular wave is a signalof which one cycle corresponds to one rotation of the input shaft.

The biphasic rectangular wave used in the conventional encoder is asignal of which one cycle corresponds to one rotation of the outputshaft whereas the biphasic rectangular wave used in the presentembodiment is a signal of which one cycle corresponds to one rotation ofthe output shaft. However, the two biphasic rectangular waves have thesame signal format.

Therefore, according to the present embodiment, the second detectionsection transmits a signal having the same format as themultiple-rotation signal of the conventional multiple-rotation absoluteencoder to the position data combination circuit. Accordingly, it ispossible to construct a multiple-rotation absolute encoder system withno battery without altering the controller of a multiple-rotationabsolute encoder system with a backup battery.

<Operation of Encoder System>

Next, the operation of the encoder system will be described using FIG.13. First, the output shaft 11 rotates with the rotation of the inputshaft 10 (step S801). In response to the rotation of the output shaft11, the second encoder 4 outputs the second detection signal (the A andB-phase signals which are biphasic pseudo-rectangular waves) to thesecond position data detection circuit 250 (step S802).

In response to the reception of the second detection signal, the secondinterpolation circuit 251 of the second position data detection circuit250 determines a corresponding phase region based on the values of the Aand B-phase signals (step S803). Subsequently, the second interpolationcircuit 251 divides the second signal by the first signal having thelarger value using the values of the A and B-phase signals (step S804).After that, the second interpolation circuit 251 reads out secondposition data corresponding to the divided value from the conversioninformation storage section 259 to detect the second position data (stepS805).

Subsequently, the second position detection circuit 252 of the secondposition data detection circuit 250 calculates a rotation count and anestimate based on the second position data detected by the secondinterpolation circuit 251 (step S806). After that, the transmissionsignal generation and output section 253 of the second position datadetection circuit 250 generates a transmission signal based on thecalculated estimate and outputs the transmission signal to the secondposition data correction circuit 262 (step S807).

On the other hand, in response to the rotation of the input shaft 10 instep S801, the first encoder 3 outputs the first detection signal to thefirst position data detection circuit 261 (step S812). In response tothe reception of the first detection signal, the first position datadetection circuit 261 detects the value of the first position datathrough interpolation (step S813).

Subsequently, the second position data correction circuit 262 correctsthe value of calculated estimate based on the value of the firstposition data detected by the first position data detection circuit 261and the estimate calculated by the second position data detectioncircuit 250 received as the transmission signal by increasing ordecreasing the value of the calculated estimate by 1 (step S821).

Subsequently, the position data combination circuit 263 generatescombined position data based on the value of the rotation count of thefirst encoder 3 corrected by the second position data correction circuit262 and the value of the first position data detected by the firstposition data detection circuit 261 (step S822) and outputs thegenerated combined position data to the controller 8 through theexternal communication circuit 265. Then, the controller 8 controls theoperation of the motor 1 through the motor control line 14.

In the conventional example, the above-described operation may beperformed as follows. A power transmission device such as a gear rotatesthe output shaft at a predetermined transmission ratio in response tothe rotation of the input shaft. The angular position of the input shaftand the angular position of the output shaft are detected, and therotation count of the input shaft is detected based on the detectedangular position of the output shaft. Then, the detected angularposition of the input shaft and the rotation count detected based on thepositional displacement of the output shaft are combined, whereby acombined position which is the absolute position in multiple rotationsof the input shaft is generated.

As one conventional example, a combined position generation method willbe described with reference to FIG. 16. As shown in FIG. 16, when thereis no shift between the information representing the rotation of theinput shaft and the information representing the rotation of the outputshaft, there is no shift between the value P1 of the first position datarepresenting the angular position of the input shaft and the rotationcount m of the input shaft detected based on the angular position of theoutput shaft. In this case, the combined position can be properlygenerated, for example, using Equation 6 below. In this case, as shownin FIG. 16, the combined position changes continuously with the rotationof the input shaft.

Combined Position=m×α+P1  (Equation 6)

In Equation 6, m is the rotation count of the input shaft calculatedbased on the angular position of the output shaft, P1 is the angularposition of the input shaft, and α is the resolution of the firstencoder. For example, in FIG. 16, the value of α is 131072.

However, in general, as shown in FIG. 17, there is a shift between theinformation representing the rotation of the input shaft and theinterference fringe representing the rotation of the output shaft. Thisshift results from the engagement between the input shaft and a gear andthe engagement between a gear and the output shaft and occursphysically.

When there is such a shift, for example, as indicated by reference signX1 in FIG. 17, the value of the rotation count m of the input shaftwhich is to be calculated as 10 may be calculated as 9. Moreover, forexample, as indicated by reference sign X2 in FIG. 17, the value of therotation count m of the input shaft which is to be calculated as 11 maybe calculated as 10. In such a case, as shown in FIG. 17, there is aproblem in that the combined position changes discontinuously with therotation of the input shaft.

Moreover, in the method above, since it is necessary to detect thepositional displacement in rotation of the input shaft and thepositional displacement in rotation of the output shaft, a device thatdetects one of the input shaft and the output shaft needs to output thedetection signal properly to the other device.

Although this output needs to be an output method capable of generatingthe combined position through this output and correcting the shift,there was a problem in that no such output method is known in theconventional art.

In the present embodiment, through the operation of the encoder systemdescribed using FIG. 13, the encoder system can correct the value of therotation count m even when there is a shift between the rotation count mand the estimate calculated based on the value P2 of the second positiondata and the value P1 of the first position data as shown in FIG. 14.Therefore, even when there is a physical shift caused by the powertransmission device 2 between the rotation of the input shaft 10 and therotation of the output shaft 11, it is possible to combine properly thedisplacement position in rotation of the input shaft 10 and thedisplacement position in rotation of the output shaft 11 to generate thecombined position which is the absolute position in multiple rotationsof the input shaft 10. Therefore, the combined position data will not bediscontinuous as shown in FIG. 17.

Moreover, the transmission signal generation and output section 253 ofthe second position data detection circuit generates the transmissionsignal representing the value of the rotation count and whether therotational position of the input shaft corresponding to the rotationcount is in the anterior half region of the rotation in one rotation ofthe input shaft or the posterior half region and outputs thetransmission signal to the second position data correction circuit 262.In this way, the second signal processing circuit 5 which is the devicethat detects one of the input shaft 10 and the output shaft 11 canproperly output the detection signal to the first signal processingcircuit 6 which is the other device.

According to the present embodiment, it is possible to provide anencoder system, a signal processing method, and a transmission signalgeneration and output device capable of outputting the detection signalproperly from the device that detects one of the input shaft and theoutput shaft to the other device, combining the combined position basedon this output, and correcting the shift.

According to the present embodiment, it is possible to provide anencoder system, a signal processing method, and a transmission signalgeneration and output device capable of combining the displacementposition in rotation of the input shaft and the displacement position inrotation of the output shaft properly even when there is a physicalshift caused by the power transmission device between the rotation ofthe input shaft and the rotation of the output shaft to generate thecombined position which is the absolute position in multiple rotationsof the input shaft.

In the present embodiment, the transmission signal generation and outputsection of the second position data detection circuit generates andoutputs the transmission signal corresponding to the rotation of theinput shaft based on the second position data detected by the secondposition data detection circuit. Therefore, it is possible to output thedetection signal properly from the device that detects one of the inputshaft and the output shaft to the other device, to combine the combinedposition based on this output, and to correct the shift.

In the present embodiment, the second position data correction circuitcorrects the second position data detected by the second position datadetection circuit, and the position data combination circuit combinesthe first position data and the corrected second position data.Therefore, an external battery for storing the absolute positioninformation is not required. Moreover, even when there is a physicalshift caused by the power transmission device between the rotation ofthe input shaft and the rotation of the output shaft, it is possible tocombine the displacement position in rotation of the input shaft and thedisplacement position in rotation of the output shaft properly togenerate the combined position which is the absolute position inmultiple rotations of the input shaft.

<Configuration for Improving Reliability and Stability>

Next, a configuration of an embodiment that improves the reliability andstability will be described using the block diagram shown in FIG. 15. Inthe embodiment described using FIGS. 1 to 10, the signal transmittedfrom the second signal processing circuit 5 is input to the first signalprocessing circuit 6 and is subjected to signal processing by asubstrate circuit in the first signal processing circuit 6. After that,the processed signal is transmitted from the first signal processingcircuit 6 to the controller 8 which is a high-order device through thecommunication line 9 which is a single cable.

If there is a failure in a component on the substrate of the firstsignal processing circuit 6, there is a fault in the connectorconnecting the substrate and the cable, or the cable connecting thefirst signal processing circuit 6 and the controller 8 is broken, it isunable to transmit the signal from the second signal processing circuit5 to the controller 8. Thus, there is a possibility that the reliabilityand standby state of the overall circuit of the encoder system isimpaired.

Therefore, the configuration shown in FIG. 15 eliminates such a problemand improves the reliability and stability. That is, the first signalprocessing circuit 6 has a configuration in which the signal from thefirst encoder 3 and the signal from the second encoder 4 are notprocessed on the same substrate but are transmitted to the controller 8through separated substrates, separate connectors, and separate cables.

For example, a first detection signal processing circuit 6A (firstprocessing circuit) that has at least the first position data detectioncircuit 261 has a first external communication circuit that outputs thefirst position data detected by the first position data detectioncircuit 261 to the controller 8 which is a high-order device through acommunication line 9A which is a first communication line. Moreover, asecond detection signal processing circuit 613 (second processingcircuit) that has at least the second position data correction circuit262 has a second external communication circuit that outputs the secondposition data detected by the second position data correction circuit262 to the controller 8 which is a high-order device through acommunication line 9B which is a second communication line. Moreover,the first detection signal processing circuit 6A and the seconddetection signal processing circuit 6B are formed on differentsubstrates.

Therefore, the detection signal detected by the first encoder 3 and thedetection signal detected by the second encoder 4 are processed bytotally different systems and are independent. Even when a failureoccurs in one of the two detection and processing sections and it isunable to transmit one of the two detection signals, the failure willnot have any influence on the transmission of the detection signal fromthe other detection section. In this way, the controller 8 can detectthe failure in one of the two detection sections by comparing the twodetection signals. Therefore, it is possible to improve the reliabilityand stability of the encoder system.

Due to space reasons, as shown by a dotted frame in the drawing, only asubstrate member of the first signal processing circuit 6 may be sharedso that the first detection signal processing circuit 6A and the seconddetection signal processing circuit 6B are completely separated in theshared substrate.

In order to improve the reliability and stability of the encoder systemas described above, the following configuration may be used. That is,the first signal processing circuit 6 that has at least the firstposition data detection circuit 261 has a third external communicationcircuit (the external communication circuit 265) that outputs the firstposition data detected by the first position data detection circuit 261to the controller 8 which is a high-order device. Moreover, the secondsignal processing circuit 5 that has at least the second position datadetection circuit 250 has a fourth external communication circuit thatoutputs the second position data detected by the second signalprocessing circuit 250 to the controller 8 which is a high-order device.Moreover, the first external communication circuit and the secondexternal communication circuit are formed on different substrates.

The first encoder 3 and the second encoder 4 may be a magnetic encoderor may be an optical encoder.

The same kinds of information are stored in the transmission ratioinformation storage sections 256 and 266, the first resolution storagesections 257 and 267, and the second resolution storage sections 258 and268, respectively. Therefore, the transmission ratio information storagesections 256 and 266, the first resolution storage sections 257 and 267,and the second resolution storage sections 258 and 268 may be configuredas an integrated section, respectively, and the respective integratedstorage sections may be provided in any one of the first and secondsignal processing circuits 6 and 5 or the encoder system. Moreover, thefirst and second signal processing circuits 6 and 5 may read outinformation from these respective integrated storage sections,respectively.

In the description above, the second position data correction circuit262 has been described to measure the rotation count of the input shaft10 based on the transmission signal input from the transmission signalgeneration and output section 253 and to correct the measured rotationcount through predetermined correction processing based on the measuredrotation count and the first position data detected by the firstposition data detection circuit.

However, the transmission signal input from the transmission signalgeneration and output section 253 may be input to the position datacombination circuit 263. In this case, the position data combinationcircuit 263 measures the rotation count of the input shaft 10 based onthe transmission signal input from the transmission signal generationand output section 253 and combines the measured rotation count and thefirst position data detected by the first position data detectioncircuit to generate the combined position data representing the rotationcount of the input shaft 10 and the angular position of the input shaft10.

Moreover, in this case, the position data combination circuit 263receives the transmission signal as the plurality of signals, detects anincrement or a decrement of the number of rotations of the input shaft10 based on a combination of the plurality of received signals, and addsthe detected increment or decrement of the number of rotations to thevalue of the rotation count of the input shaft 10 read out from therotation count storage section 264, thus calculating the rotation countof the input shaft 10.

It is assumed that these storage sections are configured by anonvolatile memory such as a hard disk device, an optomagnetic diskdevice, or a flash memory, a volatile memory such as a read-only storagemedium (for example, CD-ROM), or RAM (Random Access Memory), or acombination thereof.

The respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 shown in FIG. 6 maybe realized by special-purpose hardware and may be realized by memoriesand microprocessors.

Moreover, the respective constituent circuits of the first signalprocessing circuit 6 and the second signal processing circuit 5 may berealized by special-purpose hardware. Furthermore, the respectiveconstituent circuits of the first signal processing circuit 6 and thesecond signal processing circuit 5 may be configured by memories andCPUs (Central Processing Unit), and programs for realizing the functionsof the respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 may be loaded intothe memories and executed, whereby the functions are realized.

Next, a further embodiment will be described. The same constituentelements as the above-described embodiment will be denoted by the samereference numerals, and description thereof will be omitted orsimplified.

In the present embodiment, as shown in FIG. 5, an encoder systemincludes a motor 1, a power transmission device 2, a first encoder(first absolute position encoder) 3, a second encoder (second absoluteposition encoder) 4, an input shaft (first shaft) 10, and an outputshaft (second shaft) 11. Moreover, the encoder system includes acontroller 8 which is a high-order device, a communication line 9 whichis a communication line between the controller 8 and the first encoder3, and a motor control line 14 for connecting the controller 8 and themotor 1. Furthermore, the first encoder 3 and the second encoder 4 areconnected by a communication line 12 and a setting control line 13.

In the present embodiment, the encoder system also functions as amultiple-rotation absolute encoder as the whole encoder system using thefirst encoder 3 which is a single-rotation absolute encoder and thesecond encoder 4 which is a single-rotation absolute encoder. Therefore,this encoder system does not require an external battery for storing theabsolute position information which was required in the encoder systemof the conventional art.

In the present embodiment, the encoder system includes a first signalprocessing circuit 6 and a second signal processing circuit 5 (secondposition data detection circuit 350 described later). For example, thefirst encoder 3 has the first signal processing circuit 6 therein.Moreover, the second encoder 4 has the second signal processing circuit5 therein.

The second signal processing circuit 5 receives the second detectionsignal detected by the second encoder 4. Moreover, the second signalprocessing circuit 5 detects second position data representing thepositional displacement in the rotation of the output shaft 11 throughpredetermined signal processing (second signal processing) based on thesecond detection signal input from the second encoder 4. That is, thesecond signal processing circuit 5 interpolates the second detectionsignal to detect the second position data.

Moreover, the second signal processing circuit 5 outputs the detectedsecond position data to the first encoder 3 through the communicationline 12. When detecting the second position data, the second signalprocessing circuit 5 detects the second position data at a predeterminedresolution that is, for example, at least twice of the transmissionratio of the power transmission device 2. Here, the reason why theresolution is made at least twice of the transmission ratio is to enabledetermining whether the rotation represented by the second position datais in the anterior half region of the rotation or the posterior halfregion as will be described later.

Moreover, the first encoder 3 has the first signal processing circuit 6therein. The signal processing circuit 6 receives the second positiondata detected by the second encoder 4 through the communication line 12.Moreover, the first signal processing circuit 6 interpolates the firstdetection signal detected by the first encoder 3 to detect firstposition data representing the angular position of the input shaft 10.

Moreover, the first signal processing circuit 6 detects combinedposition data representing the rotation count of the input shaft 10 andthe angular position within one rotation of the input shaft 10 based onthe detected first position data and the input second position data.Then, the first signal processing circuit 6 outputs the detectedcombined position data to the controller 8 through the communicationline 9.

In this way, the controller 8 is able to detect the rotation count ofthe input shaft and the angular position within one rotation of theinput shaft 10 based on the combined position data from the encodersystem serving as the multiple-rotation absolute encoder. Moreover, thecontroller 8 controls the rotation of the motor 1 through the motorcontrol line 14 based on the input combined position data.

Moreover, the first signal processing circuit 6 determines whether therotation direction of the input shaft 10 and the rotation direction ofthe output shaft 11 are the same directions or the reverse directionsbased on the first position data and the second position data. That is,the first signal processing circuit 6 determines whether the rotationdirection of the input shaft 10 and the rotation direction of the outputshaft 11 are in a normal rotational relationship. Depending on thesetting of a predetermined transmission method of the power transmissiondevice 2, the normal direction in which the output shaft 11 rotates withthe rotation of the input shaft 10 may be the same direction or may bethe reverse direction.

Therefore, depending on the setting of the predetermined transmissionmethod of the power transmission device 2, the first signal processingcircuit 6 may determine whether or not the rotation direction of theinput shaft 10 and the rotation direction of the output shaft 11 are thesame directions, thus determining whether the two rotation directionsare in the normal rotational relationship. Moreover, conversely,depending on the setting of the predetermined transmission method of thepower transmission device 2, the first signal processing circuit 6 maydetermine whether or not the rotation direction of the input shaft 10and the rotation direction of the output shaft 11 are the reversedirections, thus determining whether the two rotation directions are inthe normal rotational relationship.

The first signal processing circuit 6 and the second signal processingcircuit 5 are connected by a setting control line 13. The first signalprocessing circuit 6 changes the setting values stored in a storagesection, described later, included in the second signal processingcircuit 5 through the setting control line 13.

Next, the configuration of the encoder system described using FIG. 5,particularly the configuration of the first and second signal processingcircuits 6 and 5 will be described using FIG. 18. In FIG. 18, the sameconstituent elements as those in FIG. 5 will be denoted by the samereference numerals, and description thereof will be omitted.

<Configuration of First and Second Signal Processing Circuits 6 and 5>

The second signal processing circuit 5 includes a second position datadetection circuit 350. The second position data detection circuit 350includes a second interpolation circuit 351, a second position detectioncircuit 352, a transmission signal generation and output section 353, atransmission ratio information storage section 356, a first resolutionstorage section 357, and a second resolution storage section 358. On theother hand, the first signal processing circuit 6 includes a firstposition data detection circuit 361, a second position data correctioncircuit 362, a position data combination circuit 363, a rotation countstorage section 364, an external communication circuit 365, atransmission ratio information storage section 366, a first resolutionstorage section 367, a second resolution storage section 368, a rotationdirection detection section 3610, a power supply monitoring circuit3611, a rotation direction information storage section 3612, and arotation direction information setting section 3613.

<Respective Configurations of Second Signal Processing Circuit 5>

First, the respective configurations of the second position datadetection circuit 350 of the second signal processing circuit 5 will bedescribed. In the transmission ratio information storage section 356,information representing the value of a predetermined transmission ratio(for example, a gear ratio) of the power transmission device 2connecting the first encoder 3 and the second encoder 4 is stored inadvance as transmission ratio information. In the first resolutionstorage section 357, the resolution of the first position data detectioncircuit 361 is stored in advance as a first resolution. In the secondresolution storage section 358, the resolution of the second positiondata detection circuit 350 is stored in advance as a second resolution.

The second interpolation circuit 351 interpolates the second detectionsignal input from the second encoder 4 to detect the second positiondata. The second position detection circuit 352 calculates a value ofthe integer part of a value obtained by dividing a value which isobtained by multiplying the second position data detected by the secondinterpolation circuit 351 and the transmission ratio information readout from the transmission ratio information storage section 356 by thevalue of the second resolution read out from the second resolutionstorage section 358 as the rotation count and calculates a valueobtained by multiplying a value of the fractional part of the dividedvalue and the value of the first resolution read out from the firstresolution storage section 357 as the estimate. This estimate is theestimated position data of the accurate first position data detected bythe first encoder 3, calculated based on the second detection signaldetected by the second encoder 4.

For example, the second position detection circuit 352 calculates therotation count m and the estimate s using Equations 7 and 8 below.

m=INT(n(P2/R2))  (Equation 7)

s=R1×(n(P2/R2)−m)  (Equation 8)

In Equations 7 and 8, P2 is the second position data detected by thesecond interpolation circuit 351, R1 is the first resolution stored inthe first resolution storage section 357, R2 is the second resolutionstored in the second resolution storage section 358, and n is thetransmission ratio information read out from the transmission ratioinformation storage section 356. Moreover, INT is an operator thattruncates the fractional part and extracts only the integer part.

In this way, the second position data detection circuit 350 calculatesthe rotation count of the first encoder 3 and calculates the positiondata corresponding to the first position data as the estimate based onthe interpolated value of the second detection signal detected by thesecond encoder 4 and the transmission ratio information read out fromthe transmission ratio information storage section 356 by using thesecond interpolation circuit 351 and the second position detectioncircuit 352.

The transmission signal generation and output section 353 generates atransmission signal representing the value of the rotation count of theinput shaft 10 based on the estimate calculated by the second positiondetection circuit 352 and outputs the transmission signal to the secondposition data correction circuit 362. The transmission signal generationand output section 353 generates and outputs biphasic signals which aremultiple-rotation A and B signals which are first and second rectangularsignals of which the phases are different by 90°, for example, as thetransmission signal (see FIG. 11). The biphasic signals are preferablybiphasic rectangular signals which have a rectangular waveform so as tohave resistance to external noise or the like.

In FIG. 11, when the input shaft makes one rotation, namely when thefirst position data assumes the values from 0 to 131071, themultiple-rotation A signal and the multiple-rotation B signal change inthe signal pattern of H and L; H and H; L and H, and L and L. Here, Hand L are the potentials of an electrical signal and are, for example,high and low levels, respectively. Moreover, whenever the input shaftmakes one rotation, the multiple-rotation A signal and themultiple-rotation B signal repeat the above-described signal pattern.

The multiple-rotation A and B signals generated by the transmissionsignal generation and output section 353 have the following reliabilityin accordance with the transmission ratio n and the resolution R2 of thesecond position data detection circuit 350 in one rotation of the inputshaft.

The multiple-rotation A signal is H in a period where the residue ofR2/4n is 0 to 2n and is L in the other periods. On the other hand, themultiple-rotation B signal is H in a period where the residue of R2/4nis n to 3n and is L in the other periods.

For example, the transmission signal generation and output section 353generates the above-described multiple-rotation A and B signals in thefollowing manner. The transmission signal generation and output section353 outputs H for the multiple-rotation A signal when a value obtainedby subtracting 4n from a value obtained by multiplying the resolution R2of the second position data detection circuit 350 with the estimatecalculated by the second position detection circuit 352 is within therange of 0 to 2n, and outputs L for the multiple-rotation A signal whenthe value is outside the range. Moreover, the transmission signalgeneration and output section 353 outputs H for the multiple-rotation Bsignal when a value obtained by subtracting 4n from a value obtained bymultiplying the resolution R2 of the second position data detectioncircuit 350 with the estimate calculated by the second positiondetection circuit 352 is within the range of 1n to 3n, and outputs L forthe multiple-rotation B signal when the value is outside the range.

<Respective Configurations of First Signal Processing Circuit 6>

Next, the respective configurations of the first signal processingcircuit 6 will be described. In the transmission ratio informationstorage section 366, similarly to the transmission ratio informationstorage section 356, information representing the value of apredetermined transmission ratio (for example, a gear ratio) of thepower transmission device 2 connecting the first encoder 3 and thesecond encoder 4 is stored in advance as transmission ratio information.In the first resolution storage section 367, similarly to the firstresolution storage section 357, the resolution of the first positiondata detection circuit 361 is stored in advance as a first resolution.In the second resolution storage section 368, similarly to the secondresolution storage section 358, the resolution of the second positiondata detection circuit 350 is stored in advance as a second resolution.

The first position data detection circuit 361 detects first positiondata representing the angular position of the input shaft 10 throughfirst predetermined signal processing (interpolation) based on the firstdetection signal input from the first encoder 3.

The second position data correction circuit 362 corrects the secondposition data detected by the second position data detection circuit 350through predetermined correction processing based on the second positiondata and the first position data detected by the first position datadetection circuit 361.

The position data combination circuit 363 generates combined positiondata based on the value of the rotation count of the first encoder 3corrected by the second position data correction circuit 362 and thevalue of the first position data detected by the first position datadetection circuit 361. When combining the first position data detectedby the first position data detection circuit 361 and the second positiondata detected by the second position data detection circuit 350, theposition data combination circuit 363 generates the combined positiondata based on the transmission ratio information read out from thetransmission ratio information storage section 366.

Specifically, when combining the first position data detected by thefirst position data detection circuit 361 and the second position datadetected by the second position data detection circuit 350, the positiondata combination circuit 363 generates the combined position data by apredetermined calculation method based on the transmission ratioinformation read out from the transmission ratio information storagesection 366, the first resolution read out from the first resolutionstorage section 367, and the second resolution read out from the secondresolution storage section 368.

For example, the position data combination circuit 363 calculates thecombined position data using Equation 9 below.

Combined Position Data=P1+R1×INT(n×P2/R2)  (Equation 9)

Here, P1 is the first position data, P2 is the second position data, andn is a gear ratio. Moreover, R1 is the resolution of the first positiondata detection circuit 361, and R2 is the resolution of the secondposition data detection circuit 350. Moreover, INT is an operator thattruncates the fractional part and extracts only the integer part.

The position data combination circuit 363 calculates a value obtained byadding the value of the first position data (P1) to the value of theinteger part (INT) of a value obtained by multiplying a positional ratio(P2/R2) within one rotation of the second position data detectioncircuit 350 with the gear ratio (n) as the combined position data usingEquation 9.

Moreover, the position data combination circuit 363 outputs the combinedposition data generated by the position data combination circuit 363 tothe controller 8 through the communication line 9 using the externalcommunication circuit 365.

The rotation direction detection section 3610 detects whether therotation direction of the input shaft 10 detected based on thedisplacement of the first position data and the rotation direction ofthe output shaft 11 detected based on the displacement of the secondposition data are the same directions or the reverse directions.

The external communication circuit 365 receives information representingwhether the rotation direction of the input shaft 10 and the rotationdirection of the output shaft 11 are determined to be the samedirections or the reverse directions from the controller 8 as a controlsignal. For example, the controller 8 transmits the control signal tothe external communication circuit 365 through the communication line 9.Then, in response to the reception of the control signal by the externalcommunication circuit 365, the rotation direction detection section 3610detects whether the rotation direction of the input shaft 10 and therotation direction of the output shaft 11 are the same directions or thereverse directions.

In this way, by transmitting the control signal from the controller 8,it is possible to execute the detection by the rotation directiondetection section 3610. The transmission of the control signal from thecontroller 8 may be performed every predetermined period, for example,and may be performed manually by the operation of an operator.Therefore, the encoder system of the present embodiment is able toexecute the detection by the rotation direction detection section 3610periodically or at an arbitrary time.

The power supply monitoring circuit 3611 detects whether power issupplied to the encoder system. Then, when the supply of power isdetected by the power supply monitoring circuit 3611, the rotationdirection detection section 3610 detects whether or not the rotationdirection of the input shaft 10 and the rotation direction of the outputshaft 11 are the same directions or the reverse directions. In this way,it is possible to execute the detection by the rotation directiondetection section 3610 whenever the encoder system is started up.

In the rotation direction information storage section 3612, informationrepresenting whether the rotation direction of the input shaft 10 andthe rotation direction of the output shaft 11 is stored in advance asrotation direction information. When the rotation direction informationread out from the rotation direction information storage section 3612represents that the rotation direction of the input shaft 10 and therotation direction of the output shaft 11 are the same directions, therotation direction detection section 3610 detects whether or not thedetected rotation direction of the input shaft 10 and the detectedrotation direction of the output shaft 11 are the same directions. Whenthe rotation direction information read out from the rotation directioninformation storage section 3612 represents that the rotation directionof the input shaft 10 and the rotation direction of the output shaft 11are the reverse directions, the rotation direction detection section3610 detects whether or not the detected rotation direction of the inputshaft 10 and the detected rotation direction of the output shaft 11 arethe reverse directions.

In this way, even when the rotation direction of the input shaft 10 andthe rotation direction of the output shaft 11 are the same directions orthe reverse directions, the rotation direction detection section 3610can properly detect the relationship in the rotation directions of theinput shaft 10 and the output shaft 11.

Moreover, the external communication circuit 365 receives informationrepresenting whether or not the rotation direction of the input shaft 10and the rotation direction of the output shaft 11 are the samedirections or the reverse directions from the controller 8 as settinginformation. For example, the controller 8 transmits the settinginformation to the external communication circuit 365 through thecommunication line 9. Then, the rotation direction information settingsection 3613 stores the setting information received by the externalcommunication circuit 365 in the rotation direction information storagesection 3612 as the rotation direction information.

In this way, the controller 8 can set the setting information.Therefore, even when the rotation direction of the input shaft 10 andthe rotation direction of the output shaft 11 are the same directions orthe reverse directions, it is possible to change the setting easily.Therefore, it is possible to make changes of the power transmissiondevice 2 easy.

Moreover, when the rotation direction information read out from therotation direction information storage section 3612 represents that therotation direction of the input shaft 10 and the rotation direction ofthe output shaft 11 are the same directions, and the detection resultshows that the rotation direction of the input shaft 10 and the rotationdirection of the output shaft 11 are not the same directions, therotation direction detection section 3610 transmits the detection resultto the controller 8 through the communication line 9 using the externalcommunication circuit 365 as an abnormality signal. Moreover, when therotation direction information read out from the rotation directioninformation storage section 3612 represents that the rotation directionof the input shaft 10 and the rotation direction of the output shaft 11are the reverse directions, and the detection result shows that therotation direction of the input shaft 10 and the rotation direction ofthe output shaft 11 are not the reverse directions, the rotationdirection detection section 3610 transmits the detection result to thecontroller 8 as an abnormality signal. In this way, the controller 8 orthe operator operating the controller 8 can detect abnormalities in therotation of the encoder system.

In response to reception of the abnormality signal, the controller 8stops the rotation of the motor 1 through the motor control line 14. Inthis way, by allowing the controller 8 to stop the rotation of the motor1 in response to reception of the abnormality signal, it is possible toprevent failures of the encoder system or secondary problems caused byabnormal operations.

The external communication circuit 365 executes processing forcommunication with the controller 8 through the communication line 9.Moreover, the external communication circuit 365 stores the transmissionratio information received from the controller 8 through thecommunication line 9 in the transmission ratio information storagesection 366 and stores the transmission ratio information in thetransmission ratio information storage section 356 through the settingcontrol line 13.

Furthermore, the external communication circuit 365 stores the firstresolution received from the controller 8 through the communication line9 in the first resolution storage section 367 and stores the firstresolution in the first resolution storage section 357 through thesetting control line 13. In addition, the external communication circuit365 stores the second resolution received from the controller 8 throughthe communication line 9 in the second resolution storage section 368and stores the second resolution in the second resolution storagesection 358 through the setting control line 13.

The transmission ratio information storage sections 366 and 356 arenonvolatile memories, for example. Therefore, once the value of thetransmission ratio information stored in the transmission ratioinformation storage section 366 is set, it will not be erased even whenthe encoder system is powered off. According to this configuration, itis possible to broaden the choices for the power transmission device 2and the transmission ratio of the power transmission device 2 usable inthe encoder system.

Moreover, the first resolution storage sections 357 and 367 and thesecond resolution storage sections 358 and 368 are also nonvolatilememories, for example, similarly to the transmission ratio informationstorage sections 366 and 356. Therefore, it is similarly possible tobroaden the choices for the values of the resolutions of the first andsecond position data detection circuits 361 and 350 usable in theencoder system.

In the rotation count storage section 364, the value of the rotationcount of the input shaft 10 detected by the second encoder 4 is stored.Moreover, the second position data correction circuit 362 detects thevalue of the rotation count by increasing or decreasing the value of therotation count stored in the rotation count storage section 364 by 1 inresponse to the reception of the transmission signal from the secondsignal processing circuit 5.

In the rotation count storage section 364, the value of the rotationcount of the input shaft 10 detected by the second encoder 4 at thestartup time of the encoder system is stored. For example, when theencoder system is started up, the transmission signal generation andoutput section 353 of the second signal processing circuit 5 outputs amultiple-rotation signal corresponding to the rotation count, whichrepeats the signal pattern of the multiple-rotation A and B signalsdescribed using FIG. 11 at a cycle of 1 KHz as an initial value settingsignal. Moreover, the second position data correction circuit 362 storesa value corresponding to the initial value setting signal received fromthe transmission signal generation and output section 353 of the secondsignal processing circuit 5 in the rotation count storage section 364.As a result, the rotation count information is stored in the rotationcount storage section 364.

After that, the second position data correction circuit 362 detects thevalue of the rotation count by increasing or decreasing the value of therotation count stored in the rotation count storage section 364 inresponse to the reception of the transmission signal from the secondsignal processing circuit 5.

In this way, the second signal processing circuit 5 is able to transmitthe value of the rotation count itself to the first signal processingcircuit 6 using the transmission signal which is biphasic signalrepresenting the value of the rotation count is increased or decreased.

<Details of Second Position Data Correction Circuit 362>

Next, the configuration of the second position data correction circuit362 will be described in further detail. For example, there is apossibility that a shift occurs between the first position datarepresenting the rotational position of the input shaft 10 and thesecond position data representing the rotational position of the outputshaft 11. This shift results, for example, from the engagement betweenthe input shaft 10 and the power transmission device 2 and theengagement between the power transmission device 2 and the output shaft11 and occurs physically.

Therefore, as shown in FIG. 9, there is a possibility that a shiftoccurs between the time when the rotation count (m) calculated based onthe second position data changes and the time when the first positiondata (P1) representing the rotational position of the input shaft 10changes. When there is such a shift, the position data combinationcircuit 363 is unable to generate the combined position data properly.Therefore, the second position data correction circuit 362 calculates acorrection value Δm and corrects the rotation count (m) by adding thecalculated correction value Δm to the rotation count as shown in FIG. 10so that the position data combination circuit 363 can generate thecombined position data properly even when there is such a shift.

Next, a rotation count correction method by the second position datacorrection circuit 362 will be described using FIGS. 9 and 10. In thisexample, a case in which the value of the first position data is 17 bitwill be described.

As shown in FIG. 9, the output shaft 11 rotates with the rotation of theinput shaft 10, and the rotation count m is calculated based on thevalue P2 of the second position data. Moreover, the value P1 of thefirst position data repeats the values from 0 to 131071 (=2¹⁷−1). Thatis, when the value P1 of the first position data repeats the values from0 to 131071 (=2¹⁷−1), the rotation count m changes in the order of 10,11, 12. There is a shift between the position of change (for example,the time when the value P1 of the first position data becomes 0) in theinput shaft rotation count detected based on the value P1 of the firstposition data and the time when the rotation count m changes.

As shown in FIG. 10, for example, when the value P1 of the firstposition data is within the range of 0 to 32767 (=2¹⁷×1/4−1), and thecalculated rotation count m is in the posterior half region, the secondposition data correction circuit 362 corrects the value of the rotationcount m by adding a correction value Δm (=1) to the value of therotation count m. Here, the calculated rotation count m being in theposterior half region means that the value of the calculated rotationcount m is actually m but is close to m+1.

Moreover, as shown in FIG. 10, for example, when the value P1 of thefirst position data is within the range of 98304 (=2¹⁷×3/4−1) to 131071(=2¹⁷−1), and the calculated rotation count m is in the anterior halfregion, the second position data correction circuit 362 corrects thevalue of the rotation count m by adding a correction value Δm (=−1) tothe value of the rotation count m. Here, the calculated rotation count mbeing in the anterior half region means that the value of the calculatedrotation count m is actually m but is close to m−1.

The determination as to whether the calculated rotation count m is inthe posterior half region or the anterior half region is made based onthe value of the estimate. For example, when the value of the estimatecalculated by the second position detection circuit 352 is smaller than0.5 (half cycle), the second position data correction circuit 362determines that the rotation count m is in the anterior half region.When the value of the estimate is equal to or larger than 0.5 (halfcycle), the rotation count m is determined to be in the posterior halfregion.

In FIG. 10, it was determined whether the rotational position of theinput shaft 10 detected based on the value of the rotation countdetected by the first encoder 3 in the anterior 1/4 region (0 to 32767)of the rotation in one rotation of the input shaft 10 or the posterior1/4 region (98304 to 131071). However, in order to detect the shift, itmay be determined whether the rotational position of the input shaft 10detected based on the value of the rotation count detected by the firstencoder 3 is in the anterior half region of the rotation in one rotationof the input shaft 10 or the posterior half region.

Therefore, the second position data correction circuit 362 may determinewhether the rotational position of the input shaft 10 estimated based onthe value of the estimate calculated by the second position detectioncircuit 352 is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region anddetermine whether the rotational position of the input shaft 10 detectedbased on the value of the rotation count detected by the first encoder 3is in the anterior half region of the rotation in one rotation of theinput shaft 10 or the posterior half region. Moreover, when the twodetermination results are different, the second position data correctioncircuit 362 may correct the value of the rotation count calculated bythe second position detection circuit 352.

Specifically, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 352 is in the posterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 361is in the anterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 362 correctsthe value of the rotation count calculated by the second positiondetection circuit 352 by adding 1 to the value of the rotation count.

On the other hand, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 352 is in the anterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 361is in the posterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 362 correctsthe value of the rotation count calculated by the second positiondetection circuit 352 by adding −1 to the value of the rotation count,namely by subtracting 1 from the value of the rotation count.

Then, the second position data correction circuit 362 determines whetherthe rotational position of the input shaft 10 corresponding to therotation count is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region based on thetransmission signal input from the transmission signal generation andoutput section 353 of the second position data detection circuit 350 andcorrects the value of the rotation count.

For example, as shown in FIG. 11, the multiple-rotation A and B signalschange in the signal pattern of H and L; H and H; L and H; and L and Lwhenever the input shaft makes one rotation. Therefore, when themultiple-rotation A and B signals are H and L, or H and H, respectively,the second position data correction circuit 362 determines that therotational position is in the anterior half region of the rotation inone rotation of the input shaft. On the other hand, when themultiple-rotation A and B signals are L and H, or L and L, respectively,the second position data correction circuit 362 determines that therotational position is in the posterior half region of the rotation inone rotation of the input shaft.

More specifically, when the multiple-rotation A and B signals are H andL, respectively, the second position data correction circuit 362determines that the rotational position is in the starting 1/4 region ofthe rotation in one rotation of the input shaft. Moreover, when themultiple-rotation A and B signals are L and L, respectively, the secondposition data correction circuit 362 determines that the rotationalposition is in the ending 1/4 region of the rotation in one rotation ofthe input shaft.

Moreover, the second position data correction circuit 362 detects thatthe input shaft has made one rotation by detecting that the inputmultiple-rotation A and B signals have changed sequentially in thesignal pattern of H and L; H and H; L and H; and L and L. On the otherhand, the second position data correction circuit 362 detects that theinput shaft has made one rotation in a reverse direction, namely −1rotation, by detecting that the input multiple-rotation A and B signalshave changed sequentially in the signal pattern of L and L; L and H; Hand H; and H and L.

Next, the operation of the second position data correction circuit 362and the position data combination circuit 363 will be described withrespect to cases in which the rotation direction of the input shaft 10and the rotation direction of the output shaft 11 are normally in thesame directions and are normally in the reverse directions using FIGS.19 to 22.

First, the case where the rotation direction of the input shaft 10 andthe rotation direction of the output shaft 11 are normally in the samedirections will be described using FIGS. 19 and 20. In this case, forexample, as shown in FIG. 19, when the value of the first position data(the position within one rotation is shown in the drawing) changes from0 to 131017 with the rotation of the input shaft 10, the transmissionsignal generation and output section 353 of the second encoder 4 outputsmultiple-rotation A and B signals which change sequentially in thesignal pattern of H and L; H and H; L and H; and L and L to the secondposition data correction circuit 362 of the first encoder 3.

Moreover, the second position data correction circuit 362 of the firstencoder 3 detects that the input shaft 10 has made 10 rotations based onchanges in the multiple-rotation A and B signals. After that, inresponse to a further rotation of the input shaft 10, the secondposition data correction circuit 362 similarly detects that the inputshaft 10 has made 11 rotations and 12 rotations.

In this case, the second position data correction circuit 362 correctsthe value of the rotation count at based on a correction table shown inFIG. 20. This correction is the same as the correction described usingFIG. 10.

Moreover, in this case, the position data combination circuit 363generates combined position data representing that the data have valuesof 0 to 131017 after 10 rotations, 0 to 131017 after 11 rotations, and 0to 131017 after 12 rotations.

First, the case where the rotation direction of the input shaft 10 andthe rotation direction of the output shaft 11 are normally in thereverse directions will be described using FIGS. 21 and 22. In thiscase, for example, as shown in FIG. 21, when the value of the firstposition data (the position within one rotation is shown in the drawing)changes from 0 to 131017 with the reverse rotation of the input shaft10, the transmission signal generation and output section 353 of thesecond encoder 4 outputs multiple-rotation A and B signals which changesequentially in the signal pattern of L and L; L and H; H and H; and Hand L to the second position data correction circuit 362 of the firstencoder 3.

Moreover, the second position data correction circuit 362 of the firstencoder 3 detects that the input shaft 10 has made 20 rotations based onchanges in the multiple-rotation A and B signals. After that, inresponse to a further rotation of the input shaft 10, the secondposition data correction circuit 362 similarly detects that the inputshaft 10 has made 19 rotations and 18 rotations.

As described above, when the rotation direction of the input shaft 10and the rotation direction of the output shaft 11 are reverse to eachother, the rotation count decreases from the second position data basedon the output shaft 11 whereas the rotation count increases from thefirst position data based on the input shaft 10. In this example, inorder to make the combined position data generated by the position datacombination circuit 363 comply with the rotation direction of the outputshaft 11, the first position data is converted as denoted by “correctedmotor position within one rotation” in FIG. 22.

As shown in FIG. 22, when the rotation direction of the input shaft 10and the rotation direction of the output shaft 11 are reverse to eachother, the first position data are converted so that 0 is changed to131071 and 131071 is changed to 0. That is, the first position data isconverted so that a value obtained by subtracting the value of the firstposition data from the maximum value of the first position datasubstitutes the value of the first position data.

In this case, the second position data correction circuit 362 correctsthe value of the rotation count m based on a correction table shown inFIG. 22. This correction is the same as the correction described usingFIG. 10.

Moreover, in this case, the position data combination circuit 363generates combined position data representing that the data have valuesof 0 to 131017 after 20 rotations, 0 to 131017 after 19 rotations, and 0to 131017 after 18 rotations.

<Details of Rotation Direction Detection Section 3610>

Next, a method of detecting the rotation direction of the output shaft11 based on the multiple-rotation A and B signals received by therotation direction detection section 3610 will be described using FIG.23. In FIG. 23, the rising edge of a signal is denoted by a symbol ↑ (uparrow), and the falling edge of a signal is denoted by a symbol ↓(downward arrow).

For example, when the multiple-rotation A signal is on the rising edge,and the multiple-rotation B signal is on the L level, the angularposition of the output shaft 11 is determined to be rotating in thedirection of increasing its value. Similarly, when the multiple-rotationA and B signals are respectively on the H level and rising edge, thefalling edge and H level, and the L level and falling edge, the angularposition of the output shaft 11 is determined to be rotating in thedirection of increasing its value.

On the other hand, when the multiple-rotation A and B signals arerespectively on the rising edge and H level, the L level and risingedge, the falling edge and L level, and the H level and falling edge,the angular position of the output shaft 11 is determined to be rotatingin the direction of decreasing its value.

In this way, the rotation direction detection section 3610 can detectthe rotation direction of the output shaft 11 based on the displacementof the second position data having a transmission format of themultiple-rotation A and B signals. Moreover, the rotation directiondetection section 3610 can detect whether the rotation direction of theinput shaft 10 detected based on the displacement of the first positiondata and the rotation direction of the output shaft 11 detected based onthe displacement of the second position data are the same directions orthe reverse directions.

However, according to the detection method by the rotation directiondetection section 3610 based on this direction, if the transmissionratio of the power transmission device 2 is n, for example, it is unableto know the rotation direction of the output shaft 11, namely therotation direction of the second encoder 4 unless the output shaft 11 isrotated by an angle of 360°/4n. For example, if the value of thetransmission ratio n is 100, the rotation direction becomes obscureunless the output shaft is rotated by about 0.9°. As a method ofdecreasing the value of 0.9°, by increasing the resolution of the secondposition data to be detected by the second encoder 4 (for example, theresolution is increased to 13 bit), it is possible to decrease theobscure angle to 0.04°.

The multiple-rotation A and B signals generated in this way change in asignal pattern in which they repeats H and L, H and H, L and H, and Land L twice whenever the input shaft makes one rotation, for example,rather than changing in the signal pattern in which they repeat H and L,H and H, L and H, and L and L once whenever the input shaft makes onerotation. In this manner, the transmission signal generation and outputsection 353 may generate and output a transmission signal which is abiphasic signal changing for a predetermined plural number of timescorresponding to one rotation of the input shaft 10. In this way, therotation direction detection section 3610 can detect the rotationdirection of the output shaft 11 even when the output shaft 11 isrotated by a very small angular position.

The biphasic signal of the present embodiment is generated by thetransmission signal generation and output section 353 based on thetransmission ratio information and the like stored in the transmissionratio information storage section 356. Therefore, in the encoder system,even when the transmission ratio of the power transmission device 2 hasa different value, the transmission signal generation and output section353 can easily generate a biphasic signal corresponding to the differenttransmission ratio.

The transmission signal generation and output section 353 may generateand output a transmission signal which is serial data corresponding tothe rotation of the input shaft 10 based on the second position datadetected by the second position data detection circuit 350. Moreover,the rotation direction detection section 3610 may receive thetransmission signal received from the transmission signal generation andoutput section 353 and detect the rotation direction of the output shaft11 based on the received transmission signal.

In the conventional encoder system, the output shaft is rotated by thepower transmission device such as a gear with the rotation of the inputshaft in the same direction as the rotation of the input shaft. However,the output shaft may not be rotated with the rotation of the input shaftin the same direction as the rotation of the input shaft due to afailure in the input shaft, a failure in the output shaft, a failure inthe power transmission device, and the like. For example, there is apossibility that the output shaft does not rotate with the rotation ofthe input shaft, or the output shaft rotates with the rotation of theinput shaft in the opposite direction to the rotation of the inputshaft. Such an abnormal rotation operation of the encoder system maycause secondary problems caused by the abnormal operation of the encodersystem. Therefore, in the conventional encoder system, it is necessaryto detect such an abnormal operation.

According to the present embodiment, it is possible to provide anencoder system and a signal processing method thereof, which is amultiple-rotation absolute encoder, which does not require an externalbattery for storing absolute position information, and which is capableof detecting whether or not the output shaft is rotating in the normalrotation direction with the rotation of the input shaft.

In the present embodiment, the encoder system having the powertransmission device that rotates the output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft isconfigured to: detect the first position data representing the angularposition of the input shaft and the second position data representingthe angular position of the output shaft and combine the first positiondata and the second position data. Therefore, it is possible to providean encoder system which is a multiple-rotation absolute encoder, whichdoes not require an external battery for storing absolute positioninformation. Moreover, in the present embodiment, the encoder systemdetects whether or not the rotation direction of the input shaft and therotation direction of the output shaft are the same directions or thereverse directions based on the first position data and the secondposition data. Therefore, it is possible to detect whether or not theoutput shaft is rotating in the normal rotation direction with therotation of the input shaft.

<Configuration for Improving Reliability and Stability>

Next, a configuration of an embodiment that improves the reliability andstability will be described using the block diagram shown in FIG. 15. Inthe embodiment described above, the signal transmitted from the secondsignal processing circuit 5 is input to the first signal processingcircuit 6 and is subjected to signal processing by a substrate circuitin the first signal processing circuit 6. After that, the processedsignal is transmitted from the first signal processing circuit 6 to thecontroller 8 which is a high-order device through the communication line9 which is a single cable.

If there is a failure in a component on the substrate of the firstsignal processing circuit 6, there is a fault in the connectorconnecting the substrate and the cable, or the cable connecting thefirst signal processing circuit 6 and the controller 8 is broken, it isunable to transmit the signal from the second signal processing circuit5 to the controller 8. Thus, there is a possibility that the reliabilityand standby state of the overall circuit of the encoder system isimpaired.

Therefore, the configuration shown in FIG. 15 eliminates such a problemand improves the reliability and stability. That is, the first signalprocessing circuit 6 has a configuration in which the signal from thefirst encoder 3 and the signal from the second encoder 4 are notprocessed on the same substrate but are transmitted to the controller 8through separated substrates, separate connectors, and separate cables.

For example, a first detection signal processing circuit 6A (firstprocessing circuit) that has at least the first position data detectioncircuit 361 has a first external communication circuit that outputs thefirst position data detected by the first position data detectioncircuit 361 to the controller 8 which is a high-order device through acommunication line 9A which is a first communication line. Moreover, asecond detection signal processing circuit 6B (second processingcircuit) that has at least the second position data correction circuit362 has a second external communication circuit that outputs the secondposition data detected by the second position data correction circuit362 to the controller 8 which is a high-order device through acommunication line 913 which is a second communication line. Moreover,the first detection signal processing circuit 6A and the seconddetection signal processing circuit 6B are formed on differentsubstrates.

Therefore, the detection signal detected by the first encoder 3 and thedetection signal detected by the second encoder 4 are processed bytotally different systems and are independent. Even when a failureoccurs in one of the two detection and processing sections and it isunable to transmit one of the two detection signals, the failure willnot have any influence on the transmission of the detection signal fromthe other detection section. In this way, the controller 8 can detectthe failure in one of the two detection sections by comparing the twodetection signals. Therefore, it is possible to improve the reliabilityand stability of the encoder system.

Due to space reasons, as shown by a dotted frame in the drawing, only asubstrate member of the first signal processing circuit 6 may be sharedso that the first detection signal processing circuit 6A and the seconddetection signal processing circuit 6B are completely separated in theshared substrate.

In order to improve the reliability and stability of the encoder systemas described above, the following configuration may be used. That is,the first signal processing circuit 6 that has at least the firstposition data detection circuit 361 has a third external communicationcircuit (the external communication circuit 365) that outputs the firstposition data detected by the first position data detection circuit 361to the controller 8 which is a high-order device.

Moreover, the second signal processing circuit 5 that has at least thesecond position data detection circuit 350 has a fourth externalcommunication circuit that outputs the second position data detected bythe second signal processing circuit 350 to the controller 8 which is ahigh-order device. Moreover, the first external communication circuitand the second external communication circuit are formed on differentsubstrates.

The first encoder 3 and the second encoder 4 may be a magnetic encoderor may be an optical encoder.

The same kinds of information are stored in the transmission ratioinformation storage sections 356 and 366, the first resolution storagesections 357 and 367, and the second resolution storage sections 358 and368, respectively. Therefore, the transmission ratio information storagesections 356 and 366, the first resolution storage sections 357 and 367,and the second resolution storage sections 358 and 368 may be configuredas an integrated section, respectively, and the respective integratedstorage sections may be provided in any one of the first and secondsignal processing circuits 6 and 5 or the encoder system. Moreover, thefirst and second signal processing circuits 6 and 5 may read outinformation from these respective integrated storage sections,respectively.

It is assumed that these storage sections are configured by anonvolatile memory such as a hard disk device, an optomagnetic diskdevice, or a flash memory, a volatile memory such as a read-only storagemedium (for example, CD-ROM), or RAM (Random Access Memory), or acombination thereof.

The respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 shown in FIG. 11may be realized by special-purpose hardware and may be realized bymemories and microprocessors.

Moreover, the respective constituent circuits of the first signalprocessing circuit 6 and the second signal processing circuit 5 may berealized by special-purpose hardware. Furthermore, the respectiveconstituent circuits of the first signal processing circuit 6 and thesecond signal processing circuit 5 may be configured by memories andCPUs (Central Processing Unit), and programs for realizing the functionsof the respective constituent circuits of the first signal processingcircuit 6 and the second Signal processing circuit 5 may be loaded intothe memories and executed, whereby the functions are realized.

Next, a still further embodiment will be described. The same constituentelements as the above-described embodiment will be denoted by the samereference numerals, and description thereof will be omitted orsimplified.

In the present embodiment, as shown in FIG. 24, an encoder systemincludes a motor 1, a power transmission device 2, a first encoder(first absolute position encoder) 3, a second encoder (second absoluteposition encoder) 4, an input shaft (first shaft) 10, and an outputshaft (second shaft) 11. Moreover, the encoder system includes acontroller 8 which is a high-order device, a communication line 9 whichis a communication line between the controller 8 and the first encoder3, and a motor control line 14 for connecting the controller 8 and themotor 1. Furthermore, the first encoder 3 and the second encoder 4 areconnected by a communication line 12 and a setting control line 13.

The controller 8 outputs a rotation control signal to the motor 1through the motor control line 14, thus controlling the rotation of themotor 1. The rotation control signal is a pulse wave for rotating themotor 1 which is a stepping motor, for example.

In the present embodiment, the encoder system also functions as amultiple-rotation absolute encoder as the whole encoder system using thefirst encoder 3 which is a single-rotation absolute encoder and thesecond encoder 4 which is a single-rotation absolute encoder. Therefore,this encoder system does not require an external battery for storing theabsolute position information which was required in the encoder systemof the conventional art.

In the present embodiment, the encoder system includes a first signalprocessing circuit 6 and a second signal processing circuit 5 (secondposition data detection circuit 450 described later). For example, thefirst encoder 3 has the first signal processing circuit 6 therein.Moreover, the second encoder 4 has the second signal processing circuit5 therein.

The second signal processing circuit 5 receives the second detectionsignal detected by the second encoder 4. Moreover, the second signalprocessing circuit 5 detects second position data representing thepositional displacement in the rotation of the output shaft 11 throughpredetermined signal processing (second signal processing) based on thesecond detection signal input from the second encoder 4. That is, thesecond signal processing circuit 5 interpolates the second detectionsignal to detect the second position data.

Moreover, the second signal processing circuit 5 outputs the detectedsecond position data to the first encoder 3 through the communicationline 12. When detecting the second position data, the second signalprocessing circuit 5 detects the second position data at a predeterminedresolution that is, for example, at least twice of the transmissionratio of the power transmission device 2. Here, the reason why theresolution is made at least twice of the transmission ratio is to enabledetermining whether the rotation represented by the second position datais in the anterior half region of the rotation or the posterior halfregion as will be described later.

Moreover, the first encoder 3 has the first signal processing circuit 6therein. The signal processing circuit 6 receives the second positiondata detected by the second encoder 4 through the communication line 12.Moreover, the first signal processing circuit 6 interpolates the firstdetection signal detected by the first encoder 3 to detect firstposition data representing the angular position of the input shaft 10.

Moreover, the first signal processing circuit 6 detects combinedposition data representing the rotation count of the input shaft 10 andthe angular position within one rotation of the input shaft 10 based onthe detected first position data and the input second position data.Then, the first signal processing circuit 6 outputs the detectedcombined position data to the controller 8 through the communicationline 9.

In this way, the controller 8 is able to detect the rotation count ofthe input shaft and the angular position within one rotation of theinput shaft 10 based on the combined position data from the encodersystem serving as the multiple-rotation absolute encoder. Moreover, thecontroller 8 controls the rotation of the motor 1 through the motorcontrol line 14 based on the input combined position data.

Moreover, the first signal processing circuit 6 receives the rotationcontrol signal from the controller 8 through the motor control line 14.Moreover, the first signal processing circuit 6 compares the input shaftangular position which is the angular position of the input shaft 10calculated based on the rotation control signal from the controller 8and the first position data detected by the first position datadetection circuit 461, compares the output shaft angular position whichis the angular position of the output shaft 11 calculated based on therotation control signal from the controller 8 and the second positiondata detected by the second position data detection circuit 450, anddetects a focusing lens based on a combination of the comparisonresults. Furthermore, the first signal processing circuit 6 outputinformation representing the content of the detected failure to thecontroller 8 through the communication line 9.

Next, the configuration of the encoder system described using FIG. 24,particularly the configuration of the first and second signal processingcircuits 6 and 5 will be described using FIG. 25. In FIG. 25, the sameconstituent elements as those in FIG. 24 will be denoted by the samereference numerals, and description thereof will be omitted.

<Configuration of First and Second Signal Processing Circuits 6 and 5>

The second signal processing circuit 5 includes a second position datadetection circuit 450. The second position data detection circuit 450includes a second interpolation circuit 451, a second position detectioncircuit 452, a transmission signal generation and output section 453, atransmission ratio information storage section 456, a first resolutionstorage section 457, and a second resolution storage section 458. On theother hand, the first signal processing circuit 6 includes a firstposition data detection circuit 461, a second position data correctioncircuit 462, a position data combination circuit 463, a rotation countstorage section 464, an external communication circuit 465, atransmission ratio information storage section 466, a first resolutionstorage section 467, a second resolution storage section 468, and afailure detection section 469.

<Respective Configurations of Second Signal Processing Circuit 5>

First, the respective configurations of the second position datadetection circuit 450 of the second signal processing circuit 5 will bedescribed. In the transmission ratio information storage section 456,information representing the value of a predetermined transmission ratio(for example, a gear ratio) of the power transmission device 2connecting the first encoder 3 and the second encoder 4 is stored inadvance as transmission ratio information. In the first resolutionstorage section 457, the resolution of the first position data detectioncircuit 461 is stored in advance as a first resolution. In the secondresolution storage section 458, the resolution of the second positiondata detection circuit 450 is stored in advance as a second resolution.

The second interpolation circuit 451 interpolates the second detectionsignal input from the second encoder 4 to detect the second positiondata. The second position detection circuit 452 calculates a value ofthe integer part of a value obtained by dividing a value which isobtained by multiplying the second position data detected by the secondinterpolation circuit 451 and the transmission ratio information readout from the transmission ratio information storage section 456 by thevalue of the second resolution read out from the second resolutionstorage section 458 as the rotation count and calculates a valueobtained by multiplying a value of the fractional part of the dividedvalue and the value of the first resolution read out from the firstresolution storage section 457 as the estimate. This estimate is theestimated position data of the accurate first position data detected bythe first encoder 3, calculated based on the second detection signaldetected by the second encoder 4.

For example, the second position detection circuit 452 calculates therotation count m and the estimate s using Equations 10 and 11 below.

m=INT(n(P2/R2))  (Equation 10)

s=R1×(n(P2/R2)−m)  (Equation 11)

In Equations 10 and 11, P2 is the second position data detected by thesecond interpolation circuit 451, R1 is the first resolution stored inthe first resolution storage section 457, R2 is the second resolutionstored in the second resolution storage section 458, and n is thetransmission ratio information read out from the transmission ratioinformation storage section 456. Moreover, INT is an operator thattruncates the fractional part and extracts only the integer part.

In this way, the second position data detection circuit 450 calculatesthe rotation count of the first encoder 3 and calculates the positiondata corresponding to the first position data as the estimate based onthe interpolated value of the second detection signal detected by thesecond encoder 4 and the transmission ratio information read out fromthe transmission ratio information storage section 456 by using thesecond interpolation circuit 451 and the second position detectioncircuit 452.

The transmission signal generation and output section 453 generates atransmission signal representing the value of the rotation count of theinput shaft 10 based on the estimate calculated by the second positiondetection circuit 452 and outputs the transmission signal to the secondposition data correction circuit 462. The transmission signal generationand output section 453 generates and outputs biphasic signals which aremultiple-rotation A and B signals which are first and second rectangularsignals of which the phases are different by 90°, for example, as thetransmission signal (see FIG. 11). The biphasic signals are preferablybiphasic rectangular signals which have a rectangular waveform so as tohave resistance to external noise or the like.

In FIG. 11, when the input shaft makes one rotation, namely when thefirst position data assumes the values from 0 to 131071, themultiple-rotation A signal and the multiple-rotation B signal change inthe signal pattern of H and L; H and H; L and H, and L and L. Here, Hand L are the potentials of an electrical signal and are, for example,high and low levels, respectively. Moreover, whenever the input shaftmakes one rotation, the multiple-rotation A signal and themultiple-rotation B signal repeat the above-described signal pattern.

The multiple-rotation A and B signals generated by the transmissionsignal generation and output section 453 have the following reliabilityin accordance with the transmission ratio n and the resolution R2 of thesecond position data detection circuit 450 in one rotation of the inputshaft.

The multiple-rotation A signal is H in a period where the residue ofR2/4n is 0 to 2n and is L in the other periods. On the other hand, themultiple-rotation B signal is H in a period where the residue of R2/4nis n to 3n and is L in the other periods.

For example, the transmission signal generation and output section 453generates the above-described multiple-rotation A and B signals in thefollowing manner. The transmission signal generation and output section453 outputs H for the multiple-rotation A signal when a value obtainedby subtracting 4n from a value obtained by multiplying the resolution R2of the second position data detection circuit 450 with the estimatecalculated by the second position detection circuit 452 is within therange of 0 to 2n, and outputs L for the multiple-rotation A signal whenthe value is outside the range. Moreover, the transmission signalgeneration and output section 453 outputs H for the multiple-rotation Bsignal when a value obtained by subtracting 4n from a value obtained bymultiplying the resolution R2 of the second position data detectioncircuit 450 with the estimate calculated by the second positiondetection circuit 452 is within the range of 1n to 3n, and outputs L forthe multiple-rotation B signal when the value is outside the range.

The biphasic signal made up of the multiple-rotation A and B signals ofthe present embodiment is generated by the transmission signalgeneration and output section 453 based on the transmission ratioinformation and the like stored in the transmission ratio informationstorage section 456. Therefore, in the encoder system, even when thetransmission ratio of the power transmission device 2 has a differentvalue, the transmission signal generation and output section 453 caneasily generate a biphasic signal corresponding to the differenttransmission ratio.

<Respective Configurations of First Signal Processing Circuit 6>

Next, the respective configurations of the first signal processingcircuit 6 will be described. In the transmission ratio informationstorage section 466, similarly to the transmission ratio informationstorage section 456, information representing the value of apredetermined transmission ratio (for example, a gear ratio) of thepower transmission device 2 connecting the first encoder 3 and thesecond encoder 4 is stored in advance as transmission ratio information.In the first resolution storage section 467, similarly to the firstresolution storage section 457, the resolution of the first positiondata detection circuit 461 is stored in advance as a first resolution.In the second resolution storage section 468, similarly to the secondresolution storage section 458, the resolution of the second positiondata detection circuit 450 is stored in advance as a second resolution.

The first position data detection circuit 461 detects first positiondata representing the angular position of the input shaft 10 throughfirst predetermined signal processing (interpolation) based on the firstdetection signal input from the first encoder 3.

The second position data correction circuit 462 receives the secondposition data detected by the second position data detection circuit 450from the transmission signal generation and output section 453 of thesecond position data detection circuit 450 as the multiple-rotation Aand B signals. Moreover, the second position data correction circuit 462corrects the second position data detected by the second position datadetection circuit 450 through predetermined correction processing basedon the second position data and the first position data detected by thefirst position data detection circuit 461.

The position data combination circuit 463 generates combined positiondata based on the value of the rotation count of the first encoder 3corrected by the second position data correction circuit 462 and thevalue of the first position data detected by the first position datadetection circuit 461. When combining the first position data detectedby the first position data detection circuit 461 and the second positiondata detected by the second position data detection circuit 450, theposition data combination circuit 463 generates the combined positiondata based on the transmission ratio information read out from thetransmission ratio information storage section 466.

Specifically, when combining the first position data detected by thefirst position data detection circuit 461 and the second position datadetected by the second position data detection circuit 450, the positiondata combination circuit 463 generates the combined position data by apredetermined calculation method based on the transmission ratioinformation read out from the transmission ratio information storagesection 466, the first resolution read out from the first resolutionstorage section 467, and the second resolution read out from the secondresolution storage section 468.

For example, the position data combination circuit 463 calculates thecombined position data using Equation 12 below.

Combined Position Data=P1+R1×INT(n×P2/R2)  (Equation 12)

Here, P1 is the first position data, P2 is the second position data, andn is a transmission ratio. Moreover, R1 is the resolution of the firstposition data detection circuit 461, and R2 is the resolution of thesecond position data detection circuit 450. Moreover, INT is an operatorthat truncates the fractional part and extracts only the integer part.

The position data combination circuit 463 calculates the integer part(INT) of a value obtained by multiplying a positional ratio (P2/R2)within one rotation of the second position data detection circuit 450with the gear ratio (n) and calculates a value obtained by adding thevalue of the first position data (P1) to a value obtained by multiplyingthe resolution (R1) of the first position data detection circuit 461with the value of the calculated integer part as the combined positiondata using Equation 12.

Moreover, the position data combination circuit 463 outputs thegenerated combined position data to the controller 8 through thecommunication line 9 using the external communication circuit 465.

The failure detection section 469 receives the rotation control signalfor allowing the controller 8 to control the motor 1 through the motorcontrol line 14. Moreover, the failure detection section 469 comparesthe input shaft angular position which is the angular position of theinput shaft 10 calculated based on the rotation control signal from thecontroller 8 and the first position data detected by the first positiondata detection circuit 461, compares the output shaft angular positionwhich is the angular position of the output shaft 11 calculated based onthe rotation control signal from the controller 8 and the secondposition data corrected by the second position data correction circuit462, and detects a failure based on a combination of the comparisonresults. In this way, it is possible to detect whether or not the inputshaft 10 and the output shaft 11 are rotating properly through thecontrol of the controller 8.

For example, the failure detection section 469 includes an input shaftangular position calculation section 4691, an output shaft angularposition calculation section 4692, and a comparing section 4693. Theinput shaft angular position calculation section 4691 calculates theinput shaft angular position which is the angular position of the inputshaft 10 based on the rotation control signal from the controller 8.Moreover, the output shaft angular position calculation section 4692calculates the output shaft angular position which is the angularposition of the output shaft 11 based on the rotation control signalfrom the controller 8.

When calculating the input shaft angular position based on the rotationcontrol signal from the controller 8, the input shaft angular positioncalculation section 4691 may calculate the input shaft angular positionby a predetermined calculation method based on the rotation controlsignal, the transmission ratio information read out from thetransmission ratio information storage section 466, the first resolutionread out from the first resolution storage section 467, and the secondresolution read out from the second resolution storage section 468.

Moreover, when calculating the output shaft angular position based onthe rotation control signal from the controller 8, the output shaftangular position calculation section 4692 may calculate the output shaftangular position by a predetermined calculation method based on therotation control signal, the transmission ratio information read outfrom the transmission ratio information storage section 466, the firstresolution read out from the first resolution storage section 467, andthe second resolution read out from the second resolution storagesection 468.

The comparing section 4693 compares the input shaft angular positioncalculated by the input shaft angular position calculation section 4691and the first position data detected by the first position datadetection circuit 461, compares the output shaft angular positioncalculated by the output shaft angular position calculation section 4692and the second position data corrected by the second position datacorrection circuit 462, and detects a failure based on a combination ofthe comparison results.

For example, the comparing section 4693 of the failure detection section469 detects whether or not the input shaft angular position is identicalto the first position data and detects whether or not the output shaftangular position is identical to the second position data. Moreover,when the detection result shows that the input shaft angular position isnot identical to the first position data, and the output shaft angularposition is identical to the second position data, the comparing section4693 of the failure detection section 469 outputs a signal to thecontroller 8, representing that there is a failure in an inputshaft-side device which is any one of the first encoder 3 and the firstposition data detection circuit 461 or a combination thereof. On theother hand, when the detection result shows that the input shaft angularposition is identical to the first position data, and the output shaftangular position is not identical to the second position data, thecomparing section 4693 of the failure detection section 469 outputs asignal to the controller 8, representing that there is a failure in anoutput shaft-side device which is any one of the power transmissiondevice 2, the second encoder 4, and the second position data detectioncircuit 450 or a combination thereof.

Moreover, when the input shaft angular position is not identical to thefirst position data, and the output shaft angular position is notidentical to the second position data, the comparing section 4693 of thefailure detection section 469 outputs a signal indicative of a failureto the controller 8.

In the case of the signal indicative of a failure output when the inputshaft angular position is not identical to the first position data, andthe output shaft angular position is not identical to the secondposition data, there is a possibility that there is a failure in any oneof the motor 1, the controller 8, the first encoder 3, the firstposition data detection circuit 461, the power transmission device 2,the second encoder 4, and the second position data detection circuit 450or a combination thereof.

As described above, the comparing section 4693 of the failure detectionsection 469 outputs a signal indicative of a failure in the inputshaft-side device, a signal indicative of a failure in the outputshaft-side device, or a signal indicative of a failure to the controller8. In this way, the controller 8 is able to detect whether or not theinput shaft and the output shaft are rotating properly based on therotation control signal and detect the device in which the failure hasoccurred. Therefore, when repairing the failed device, the userperforming the repairing can perform the repair quickly since the usercan know the failed device in the encoder system.

Moreover, when detecting whether or not the input shaft angular positionis identical to the first position data and whether or not the outputshaft angular position is identical to the second position data, thecomparing section 4693 of the failure detection section 469 detects thatthe input shaft angular position is identical to the first position dataif a difference therebetween is equal to or smaller than a predeterminedfirst allowable amount and detects that they are not identical if thedifference is not equal to or smaller than the first allowable amount.Moreover, when detecting whether or not the input shaft angular positionis identical to the first position data and whether or not the outputshaft angular position is identical to the second position data, thecomparing section 4693 of the failure detection section 469 detects thatthe input shaft angular position is identical to the second positiondata if a difference therebetween is equal to or smaller than apredetermined second allowable amount and detects that they are notidentical if the difference is not equal to or smaller than the secondallowable amount. The first allowable amount and the second allowableamount are rotation amounts corresponding to the half rotation or the1/4 rotation of the input shaft 10, for example.

In general, there is not a great shift between the input shaft angularposition and the first position data. However, a small shift may occurdue to detection errors or the like. Even when there is such a shift, asdescribed above, by detecting that the input shaft angular position isidentical to the first position data if a difference therebetween isequal to or smaller than a predetermined first allowable amount anddetects that they are not identical if the difference is not equal to orsmaller than the first allowable amount, it is possible to detectproperly whether they are identical or not considering the errors. Thesame can be applied to the case of comparing the output shaft angularposition and the second position data.

Moreover, the failure detection section 469 includes a position datacomparing and collating circuit 4694. The position data comparing andcollating circuit 4694 calculates position data corresponding to thefirst position data to be detected by the first position data detectioncircuit 461 as an estimate based on the second position data detected bythe second position data detection circuit 450, namely the secondposition data corrected by the second position data correction circuit462 and the transmission ratio information read out from thetransmission ratio information storage section 466. Moreover, theposition data comparing and collating circuit 4694 calculates adifference between the calculated estimate and the first position datadetected by the first position data detection circuit 461 as an errorestimate.

Moreover, the position data comparing and collating circuit 4694determines whether or not the calculated error estimate is within apredetermined range of values, and when the determination result showsthat the calculated error estimate is not within the predetermined rangeof values, outputs a signal to the controller 8, representing that thefirst position data detected by the first position data detectioncircuit 461 is not identical to the second position data detected by thesecond position data detection circuit 450) or the second position datacorrected by the second position data correction circuit 462).

When it is detected that the input shaft and the output shaft are notrotating properly in response to the reception of the signal indicativeof a failure in the input shaft-side device, the signal indicative of afailure in the output shaft-side device, or the signal indicative of afailure from the comparing section 4693 of the failure detection section469, the controller 8 stops the rotation of the motor 1 through themotor control line 14.

Moreover, in response to the reception of the signal representing thatthe first position data detected by the first position data detectioncircuit 461 is not identical to the second position data detected by thesecond position data detection circuit 450 (the second position datacorrected by the second position data correction circuit 462) from theposition data comparing and collating circuit 4694 of the failuredetection section 469, the controller 8 stops the rotation of the motor1 through the motor control line 14.

In this way, by allowing the controller 8 to stop the rotation of themotor 1 in response to detecting that the input shaft and the outputshaft are not properly rotating, it is possible to prevent failures ofthe encoder system or secondary problems caused by abnormal operations.

The external communication circuit 465 executes processing forcommunication with the controller 8 through the communication line 9.Moreover, the external communication circuit 465 stores the transmissionratio information received from the controller 8 through thecommunication line 9 in the transmission ratio information storagesection 466 and stores the transmission ratio information in thetransmission ratio information storage section 456 through the settingcontrol line 13.

Furthermore, the external communication circuit 465 stores the firstresolution received from the controller 8 through the communication line9 in the first resolution storage section 467 and stores the firstresolution in the first resolution storage section 457 through thesetting control line 13. In addition, the external communication circuit465 stores the second resolution received from the controller 8 throughthe communication line 9 in the second resolution storage section 468and stores the second resolution in the second resolution storagesection 458 through the setting control line 13.

The transmission ratio information storage sections 466 and 456 arenonvolatile memories, for example. Therefore, once the value of thetransmission ratio information stored in the transmission ratioinformation storage section 466 is set, it will not be erased even whenthe encoder system is powered off. According to this configuration, itis possible to broaden the choices for the power transmission device 2and the transmission ratio of the power transmission device 2 usable inthe encoder system.

Moreover, the first resolution storage sections 457 and 467 and thesecond resolution storage sections 458 and 468 are also nonvolatilememories, for example, similarly to the transmission ratio informationstorage sections 466 and 456. Therefore, it is similarly possible tobroaden the choices for the values of the resolutions of the first andsecond position data detection circuits 461 and 450 usable in theencoder system.

In the rotation count storage section 464, the value of the rotationcount of the input shaft 10 detected by the second encoder 4 is stored.Moreover, the second position data correction circuit 462 detects thevalue of the rotation count by increasing or decreasing the value of therotation count stored in the rotation count storage section 464 by 1 inresponse to the reception of the transmission signal from the secondsignal processing circuit 5.

In the rotation count storage section 464, the value of the rotationcount of the input shaft 10 detected by the second encoder 4 at thestartup time of the encoder system is stored. For example, when theencoder system is started up, the transmission signal generation andoutput section 453 of the second signal processing circuit 5 outputs amultiple-rotation signal corresponding to the rotation count, whichrepeats the signal pattern of the multiple-rotation A and B signalsdescribed using FIG. 11 at a cycle of 1 KHz as an initial value settingsignal. Moreover, the second position data correction circuit 462 storesa value corresponding to the initial value setting signal received fromthe transmission signal generation and output section 453 of the secondsignal processing circuit 5 in the rotation count storage section 464.As a result, the rotation count information is stored in the rotationcount storage section 464.

After that, the second position data correction circuit 462 detects thevalue of the rotation count by increasing or decreasing the value of therotation count stored in the rotation count storage section 464 inresponse to the reception of the transmission signal from the secondsignal processing circuit 5.

In this way, the second signal processing circuit 5 is able to transmitthe value of the rotation count itself to the first signal processingcircuit 6 using the transmission signal which is biphasic signalrepresenting the value of the rotation count is increased or decreased.

<Details of Position Data Combination Circuit 463 and Position DataComparing and Collating Circuit 4694>

Next, processing executed by the position data combination circuit 463and the position data comparing and collating circuit 4694 will bedescribed in detail using FIG. 26. In this description, it is assumedthat the resolution of the first position data detection circuit 461 is13 bit, and the resolution of the second position data detection circuit450 (the second position detection circuit 452) is 11 bit. That is, thefirst position data detection circuit 461 output the first position datawhich is an integer value within the range of 0 to 8191 (=2¹³−1).Moreover, the second position data detection circuit 450 outputs thesecond position data which is an integer value within the range of 0 to2047 (=2¹¹−1). Moreover, it is assumed that the transmission ratio ofthe power transmission device 2 is 100, and the transmission ratioinformation having a value of 100 is stored in advance in thetransmission ratio information storage section 466.

Here, a case in which the first position data detection circuit 461outputs 1000 as the value of the first position data will be describedas an example. Moreover, a case in which the second position datadetection circuit 450 outputs 310 as the value of the second positiondata and the second position data correction circuit 462 also outputs310 as the value of the second position data will be described.Moreover, it is assumed that the rotation count of the input shaft 10 is15.

First, the position data combination circuit 463 will be described. Theposition data combination circuit 463 calculates the combined positiondata using Equation 12 described above. In this case, since the value ofthe first position data P1 is 1000, the value of the second positiondata P2 is 310, the value of the transmission ratio n is 100, the valueof the resolution R1 of the first position data detection circuit 461 is8192, and the value of the resolution R2 of the second position datadetection circuit 450 is 2048, the position data combination circuit 463calculates 123865 as the value of the combined position data usingEquation 12.

Next, the position data comparing and collating circuit 4694 will bedescribed. First, the position data comparing and collating circuit 4694calculates the estimate using Equation 13 below.

Estimate=mod(P2/R2)×n×R1  (Equation 13)

Here, R1 is the resolution of the first position data detection circuit461. Moreover, mod is an operator that truncates the integer part andextracts only the fractional part. In Equation 13, the same symbols asused in Equation 12 represent the same physical quantities as those ofEquation 12.

The position data comparing and collating circuit 4694 calculates avalue obtained by multiplying the value of the fractional part of thepositional ratio (P2/R2) within one rotation of the second position datadetection circuit 450 with the transmission ratio (n) and the resolutionR1 of the first position data detection circuit 461 as the estimateusing Equation 13.

In this case, since the value of the second position data P2 is 310, thevalue of the resolution R2 of the second position data detection circuit450 is 2048, the value of the transmission ratio n is 100, and the valueof the resolution R1 of the first position data detection circuit 461 is8192, the position data comparing and collating circuit 4694 calculates1024 as the value of the estimate using Equation 13.

Subsequently, the position data comparing and collating circuit 4694calculates an error estimate using Equation 14 below.

Error Estimate=Estimate−P1  (Equation 14).

Here, the estimate in Equation 14 is the estimate calculated by Equation13. The position data comparing and collating circuit 4694 calculates adifference between the calculated estimate and the first position dataP1 as the error estimate using Equation 14. In this case, since thevalue of the estimate is 1024, and the value of the first position dataP1 is 1000, the position data comparing and collating circuit 4694calculates 24 as the value of the error estimate using Equation 14.

Subsequently, the position data comparing and collating circuit 4694determines whether or not the absolute value of the error estimatecalculated by Equation 14 is equal to or smaller than, for example, 1/8of the resolution R1 of the first position data detection circuit 461.In this case, since the value of the calculated error estimate is 24,the value of the resolution R1 of the first position data detectioncircuit 461 is 8192, and the absolute value of the calculated errorestimate is equal to or smaller than 1/8 of the resolution R1 of thefirst position data detection circuit 461, the position data comparingand collating circuit 4694 outputs normal as the determination result.If the absolute value of the calculated error estimate is not equal toor smaller than 1/8 of the resolution R1 of the first position datadetection circuit 461, the position data comparing and collating circuit4694 outputs abnormal as the determination result. Moreover, when thedetermination result indicates abnormalities, the position datacomparing and collating circuit 4694 output a signal to the controller8, representing that the first position data detected by the firstposition data detection circuit 461 is not identical to the secondposition data detected by the second position data detection circuit 450(or the second position data corrected by the second position datacorrection circuit 462).

<Details of Second Position Data Correction Circuit 462>

Next, the configuration of the second position data correction circuit462 will be described in further detail using FIGS. 9 and 10. Forexample, there is a possibility that a shift occurs between the firstposition data representing the rotational position of the input shaft 10and the second position data representing the rotational position of theoutput shaft 11. This shift results, for example, from the engagementbetween the input shaft 10 and the power transmission device 2 and theengagement between the power transmission device 2 and the output shaft11 and occurs physically.

Therefore, as shown in FIG. 9, there is a possibility that a shiftoccurs between the time when the rotation count (m) calculated based onthe second position data changes and the time when the first positiondata (P1) representing the rotational position of the input shaft 10changes. When there is such a shift, the position data combinationcircuit 463 is unable to generate the combined position data properly.Therefore, the second position data correction circuit 462 calculates acorrection value Δm and corrects the rotation count (m) by adding thecalculated correction value Δm to the rotation count as shown in FIG. 10so that the position data combination circuit 463 can generate thecombined position data properly even when there is such a shift.

Next, a rotation count correction method by the second position datacorrection circuit 462 will be described using FIGS. 9 and 10. In thisexample, a case in which the value of the first position data is 17 bitwill be described.

As shown in FIG. 9, the output shaft 11 rotates with the rotation of theinput shaft 10, and the rotation count m is calculated based on thevalue P2 of the second position data. Moreover, the value P1 of thefirst position data repeats the values from 0 to 131071 (=2¹⁷−1). Thatis, when the value P1 of the first position data repeats the values from0 to 131071 (=2¹⁷−1), the rotation count m changes in the order of 10,11, 12. There is a shift between the position of change (for example,the time when the value P1 of the first position data becomes 0) in theinput shaft rotation count detected based on the value P1 of the firstposition data and the time when the rotation count m changes.

As shown in FIG. 10, for example, when the value P1 of the firstposition data is within the range of 0 to 32767 (=2¹⁷×1/4−1), and thecalculated rotation count m is in the posterior half region, the secondposition data correction circuit 462 corrects the value of the rotationcount m by adding a correction value Δm (=1) to the value of therotation count m. Here, the calculated rotation count m being in theposterior half region means that the value of the calculated rotationcount m is actually m but is close to m+1.

Moreover, as shown in FIG. 10, for example, when the value P1 of thefirst position data is within the range of 98304 (=2¹⁷×3/4−1) to 131071(=2¹⁷−1), and the calculated rotation count m is in the anterior halfregion, the second position data correction circuit 462 corrects thevalue of the rotation count m by adding a correction value Δm (=−1) tothe value of the rotation count m. Here, the calculated rotation count mbeing in the anterior half region means that the value of the calculatedrotation count in is actually m but is close to m−1.

The determination as to whether the calculated rotation count m is inthe posterior half region or the anterior half region is made based onthe value of the estimate. For example, when the value of the estimatecalculated by the second position detection circuit 452 is smaller than0.5 (half cycle), the second position data correction circuit 462determines that the rotation count m is in the anterior half region.When the value of the estimate is equal to or larger than 0.5 (halfcycle), the rotation count m is determined to be in the posterior halfregion.

In FIG. 10, it was determined whether the rotational position of theinput shaft 10 detected based on the value of the rotation countdetected by the first encoder 3 in the anterior 1/4 region (0 to 32767)of the rotation in one rotation of the input shaft 10 or the posterior1/4 region (98304 to 131071). However, in order to detect the shift, itmay be determined whether the rotational position of the input shaft 10detected based on the value of the rotation count detected by the firstencoder 3 is in the anterior half region of the rotation in one rotationof the input shaft 10 or the posterior half region.

Therefore, the second position data correction circuit 462 may determinewhether the rotational position of the input shaft 10 estimated based onthe value of the estimate calculated by the second position detectioncircuit 452 is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region anddetermine whether the rotational position of the input shaft 10 detectedbased on the value of the rotation count detected by the first encoder 3is in the anterior half region of the rotation in one rotation of theinput shaft 10 or the posterior half region. Moreover, when the twodetermination results are different, the second position data correctioncircuit 462 may correct the value of the rotation count calculated bythe second position detection circuit 452.

Specifically, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 452 is in the posterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 461is in the anterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 462 correctsthe value of the rotation count calculated by the second positiondetection circuit 452 by adding 1 to the value of the rotation count.

On the other hand, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 452 is in the anterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 461is in the posterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 462 correctsthe value of the rotation count calculated by the second positiondetection circuit 452 by adding −1 to the value of the rotation count,namely by subtracting 1 from the value of the rotation count.

Then, the second position data correction circuit 462 determines whetherthe rotational position of the input shaft 10 corresponding to therotation count is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region based on thetransmission signal input from the transmission signal generation andoutput section 453 of the second position data detection circuit 450 andcorrects the value of the rotation count.

For example, as shown in FIG. 11, the multiple-rotation A and B signalschange in the signal pattern of H and L; H and H; L and H; and L and Lwhenever the input shaft makes one rotation. Therefore, when themultiple-rotation A and B signals are H and L, or H and H, respectively,the second position data correction circuit 462 determines that therotational position is in the anterior half region of the rotation inone rotation of the input shaft. On the other hand, when themultiple-rotation A and B signals are L and H, or L and L, respectively,the second position data correction circuit 462 determines that therotational position is in the posterior half region of the rotation inone rotation of the input shaft.

More specifically, when the multiple-rotation A and B signals are H andL, respectively, the second position data correction circuit 462determines that the rotational position is in the starting 1/4 region ofthe rotation in one rotation of the input shaft. Moreover, when themultiple-rotation A and B signals are L and L, respectively, the secondposition data correction circuit 462 determines that the rotationalposition is in the ending 1/4 region of the rotation in one rotation ofthe input shaft.

Moreover, the second position data correction circuit 462 detects thatthe input shaft has made one rotation by detecting that the inputmultiple-rotation A and B signals have changed sequentially in thesignal pattern of H and L; H and H; L and H; and L and L. On the otherhand, the second position data correction circuit 462 detects that theinput shaft has made one rotation in a reverse direction, namely −1rotation, by detecting that the input multiple-rotation A and B signalshave changed sequentially in the signal pattern of L and L; L and H; Hand H; and H and L.

In the conventional encoder system, the input shaft rotates under thecontrol of the controller which is a high-order control device, and theoutput shaft is rotated with the rotation of the input shaft by thepower transmission device. However, due to a failure in the input shaft,a failure in the output shaft, a failure in the power transmissiondevice, and the like, the input shaft may not rotate properly under thecontrol of the controller, and the output shaft may not rotate properlyeven when the input shaft rotates properly under the control of thecontroller. Such an abnormal rotation operation of the encoder systemmay cause secondary problems caused by the abnormal operation of theencoder system. Therefore, in the encoder system, it is necessary todetect such an abnormal operation.

According to the present embodiment, it is possible to provide anencoder system and a signal processing method capable of detectingwhether or not the input shaft and the output shaft are rotatingproperly under the control of the controller.

In the present embodiment, the encoder system having the powertransmission device that rotates the output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft isconfigured to: detect the first position data representing the angularposition of the input shaft and the second position data representingthe angular position of the output shaft and combine the first positiondata and the second position data. Therefore, it is possible to providean encoder system which is a multiple-rotation absolute encoder, whichdoes not require an external battery for storing absolute positioninformation.

In the present embodiment, the failure detection section of the encodersystem compares the input shaft angular position which is the angularposition of the input shaft calculated based on the rotation controlsignal from the controller and the first position data detected by thefirst position data detection circuit. Moreover, in the presentembodiment, the failure detection section compares the output shaftangular position which is the angular position of the output shaftcalculated based on the rotation control signal and the second positiondata detected by the second position data detection circuit. Moreover, afailure is detected based on a combination of the comparison results.Therefore, it is possible to detect whether or not the input shaft andthe output shaft are rotating properly under the control of thecontroller.

<Configuration for Improving Reliability and Stability>

Next, a configuration of an embodiment that improves the reliability andstability will be described using the block diagram shown in FIG. 15. Inthe embodiment described above, the signal transmitted from the secondsignal processing circuit 5 is input to the first signal processingcircuit 6 and is subjected to signal processing by a substrate circuitin the first signal processing circuit 6. After that, the processedsignal is transmitted from the first signal processing circuit 6 to thecontroller 8 which is a high-order device through the communication line9 which is a single cable.

If there is a failure in a component on the substrate of the firstsignal processing circuit 6, there is a fault in the connectorconnecting the substrate and the cable, or the cable connecting thefirst signal processing circuit 6 and the controller 8 is broken, it isunable to transmit the signal from the second signal processing circuit5 to the controller 8. Thus, there is a possibility that the reliabilityand standby state of the overall circuit of the encoder system isimpaired.

Therefore, the configuration shown in FIG. 15 eliminates such a problemand improves the reliability and stability. That is, the first signalprocessing circuit 6 has a configuration in which the signal from thefirst encoder 3 and the signal from the second encoder 4 are notprocessed on the same substrate but are transmitted to the controller 8through separated substrates, separate connectors, and separate cables.

For example, a first detection signal processing circuit 6A (firstprocessing circuit) that has at least the first position data detectioncircuit 461 has a first external communication circuit that outputs thefirst position data detected by the first position data detectioncircuit 461 to the controller 8 which is a high-order device through acommunication line 9A which is a first communication line. Moreover, asecond detection signal processing circuit 6B (second processingcircuit) that has at least the second position data correction circuit462 has a second external communication circuit that outputs the secondposition data detected by the second position data correction circuit462 to the controller 8 which is a high-order device through acommunication line 9B which is a second communication line. Moreover,the first detection signal processing circuit 6A and the seconddetection signal processing circuit 6B are formed on differentsubstrates.

Therefore, the detection signal detected by the first encoder 3 and thedetection signal detected by the second encoder 4 are processed bytotally different systems and are independent. Even when a failureoccurs in one of the two detection and processing sections and it isunable to transmit one of the two detection signals, the failure willnot have any influence on the transmission of the detection signal fromthe other detection section. In this way, the controller 8 can detectthe failure in one of the two detection sections by comparing the twodetection signals. Therefore, it is possible to improve the reliabilityand stability of the encoder system.

Due to space reasons, as shown by a dotted frame in the drawing, only asubstrate member of the first signal processing circuit 6 may be sharedso that the first detection signal processing circuit 6A and the seconddetection signal processing circuit 6B are completely separated in theshared substrate.

In order to improve the reliability and stability of the encoder systemas described above, the following configuration may be used. That is,the first signal processing circuit 6 that has at least the firstposition data detection circuit 461 has a third external communicationcircuit (the external communication circuit 465) that outputs the firstposition data detected by the first position data detection circuit 461to the controller 8 which is a high-order device.

Moreover, the second signal processing circuit 5 that has at least thesecond position data detection circuit 450 has a fourth externalcommunication circuit that outputs the second position data detected bythe second signal processing circuit 450 to the controller 8 which is ahigh-order device. Moreover, the first external communication circuitand the second external communication circuit are formed on differentsubstrates.

The first encoder 3 and the second encoder 4 may be a magnetic encoderor may be an optical encoder.

In the encoder system described above, although the first signalprocessing circuit 6 has been described to have the failure detectionsection 469, the present invention is not limited to this.

For example, the controller 8 may have the failure detection section469. In this case, for example, the first position data detectioncircuit 461 of the first signal processing circuit 6 may transmit thedetected first position data to the controller 8 through thecommunication line 9 using the external communication circuit 465.Moreover, the second position data correction circuit 462 of the firstsignal processing circuit 6 may transmit the second position data to thecontroller 8 through the communication line 9 using the externalcommunication circuit 465.

Then, the failure detection section 469 of the controller 8 maycalculate the input shaft angular position and the output shaft angularposition, compare the calculated input shaft angular position with thereceived first position data, compare the calculated output shaftangular position with the received second position data, and detect afailure based on a combination of the comparison results. That is, thecontroller 8 may include the input shaft angular position calculationsection 4691, the output shaft angular position calculation section4692, and the comparing section 4693 described using FIG. 25.

Moreover, the controller 8 may calculate the input shaft angularposition and the output shaft angular position and transmit thecalculated input shaft angular position and output shaft angularposition to the failure detection section 469 of the first signalprocessing circuit 6 through the communication line 9 using the externalcommunication circuit 465. Then, the failure detection section 469 ofthe first signal processing circuit 6 may compare the received inputshaft angular position with the first position data, compare thereceived output shaft angular position with the second position data,and detect a failure based on a combination of the comparison results.That is, the controller 8 may include the input shaft angular positioncalculation section 4691 and the output shaft angular positioncalculation section 4692 described using FIG. 25, and the failuredetection section 469 of the first signal processing circuit 6 may havethe comparing section 4693.

In the description above, although the second position data detectioncircuit 450 and the second position data correction circuit 462 havebeen described to be different configurations, the second position datadetection circuit 450 and the second position data correction circuit462 may be integrated as the second position data detection circuit 450.

The same kinds of information are stored in the transmission ratioinformation storage sections 456 and 466, the first resolution storagesections 457 and 467, and the second resolution storage sections 458 and468, respectively. Therefore, the transmission ratio information storagesections 456 and 466, the first resolution storage sections 457 and 467,and the second resolution storage sections 458 and 468 may be configuredas an integrated section, respectively, and the respective integratedstorage sections may be provided in any one of the first and secondsignal processing circuits 6 and 5 or the encoder system. Moreover, thefirst and second signal processing circuits 6 and 5 may read outinformation from these respective integrated storage sections,respectively.

It is assumed that these storage sections are configured by anonvolatile memory such as a hard disk device, an optomagnetic diskdevice, or a flash memory, a volatile memory such as a read-only storagemedium (for example, CD-ROM), or RAM (Random Access Memory), or acombination thereof.

The respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 shown in FIG. 25may be realized by special-purpose hardware and may be realized bymemories and microprocessors.

Moreover, the respective constituent circuits of the first signalprocessing circuit 6 and the second signal processing circuit 5 may berealized by special-purpose hardware. Furthermore, the respectiveconstituent circuits of the first signal processing circuit 6 and thesecond signal processing circuit 5 may be configured by memories andCPUs (Central Processing Unit), and programs for realizing the functionsof the respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 may be loaded intothe memories and executed, whereby the functions are realized.

Next, a still further embodiment will be described. The same constituentelements as the above-described embodiment will be denoted by the samereference numerals, and description thereof will be omitted orsimplified.

In the present embodiment, as shown in FIG. 5, an encoder systemincludes a motor 1, a power transmission device 2, a first encoder(first absolute position encoder) 3, a second encoder (second absoluteposition encoder) 4, an input shaft (first shaft) 10, and an outputshaft (second shaft) 11. Moreover, the encoder system includes acontroller 8 which is a high-order device, a communication line 9 whichis a communication line between the controller 8 and the first encoder3, and a motor control line 14 for connecting the controller 8 and themotor 1. Furthermore, the first encoder 3 and the second encoder 4 areconnected by a communication line 12 and a setting control line 13.

Here, for example, it is assumed that the first encoder 3 outputs Nsignals for one rotation, the second encoder 4 outputs M signals for onerotation, and the power transmission device 2 connects the input shaft10 and the output shaft 11 at a ratio of 1:N. In this case, since thesecond encoder 4 rotates by one digit whenever the first encoder 3 makesone rotation, it is possible to detect the rotation count of the inputshaft 10 and to detect the angular position of the input shaft 10.Therefore, this encoder system is capable of detecting N×M rotationalpositions, namely the absolute position in the rotation of the inputshaft 10 until the output shaft 11 makes M rotations.

That is, this encoder system functions as a multiple-rotation absoluteencoder as the whole encoder system using the first encoder 3 which is asingle-rotation absolute encoder and the second encoder 4 which is asingle-rotation absolute encoder.

In the present embodiment, the encoder system includes a first signalprocessing circuit 6 and a second signal processing circuit 5 (secondposition data detection circuit 550 described later). For example, thefirst encoder 3 has the first signal processing circuit 6 therein.Moreover, the second encoder 4 has the second signal processing circuit5 therein.

The second signal processing circuit 5 receives the second detectionsignal detected by the second encoder 4. Moreover, the second signalprocessing circuit 5 detects second position data representing theangular position of the output shaft 11 through predetermined signalprocessing (second signal processing) based on the second detectionsignal input from the second encoder 4. That is, the second signalprocessing circuit 5 interpolates the second detection signal to detectthe second position data.

Moreover, the second signal processing circuit 5 outputs the detectedsecond position data to the first encoder 3 through the communicationline 12. When detecting the second position data, the second signalprocessing circuit 5 detects the second position data at a predeterminedresolution that is, for example, at least twice of the transmissionratio of the power transmission device 2. Here, the reason why theresolution is made at least twice of the transmission ratio is to enabledetermining whether the rotation represented by the second position datais in the anterior half region of the rotation or the posterior halfregion as will be described later.

Moreover, the first encoder 3 has the first signal processing circuit 6therein. The first signal processing circuit 6 receives the secondposition data detected by the second encoder 4 through the communicationline 12. Moreover, the first signal processing circuit 6 interpolatesthe first detection signal detected by the first encoder 3 to detectfirst position data representing the angular position of the input shaft10.

Moreover, the first signal processing circuit 6 detects combinedposition data representing the rotation count of the input shaft 10 andthe angular position within one rotation of the input shaft 10 based onthe detected first position data and the input second position data.Then, the first signal processing circuit 6 outputs the detectedcombined position data to the controller 8 through the communicationline 9.

In this way, the controller 8 is able to detect the rotation count ofthe input shaft and the angular position within one rotation of theinput shaft 10 based on the combined position data from the encodersystem serving as the multiple-rotation absolute encoder. Moreover, thecontroller 8 controls the rotation of the motor 1 through the motorcontrol line 14 based on the input combined position data.

The first signal processing circuit 6 and the second signal processingcircuit 5 are connected by a setting control line 13. The first signalprocessing circuit 6 changes the setting values stored in a storagesection, described later, included in the second signal processingcircuit 5 through the setting control line 13.

Next, the configuration of the encoder system described using FIG. 5,particularly the configuration of the first and second signal processingcircuits 6 and 5 will be described using FIG. 27. In FIG. 27, the sameconstituent elements as those in FIG. 5 will be denoted by the samereference numerals, and description thereof will be omitted.

<Configuration of First and Second Signal Processing Circuits 6 and 5>

The second signal processing circuit 5 includes a second position datadetection circuit 550. The second position data detection circuit 550includes a second interpolation circuit 551, a second position detectioncircuit 552, a transmission signal generation and output section 553, atransmission ratio information storage section 556, a first resolutionstorage section 557, and a second resolution storage section 558. On theother hand, the first signal processing circuit 6 includes a firstposition data detection circuit 561, a second position data correctioncircuit 562, a position data combination circuit 563, a rotation countstorage section 564, an external communication circuit 565, atransmission ratio information storage section 566, a first resolutionstorage section 567, a second resolution storage section 568, a rotationdirection detection section 5610, a power supply monitoring circuit5611, a rotation direction information storage section 5612, and arotation direction information setting section 5613.

<Respective Configurations of Second Signal Processing Circuit 5>

First, the respective configurations of the second position datadetection circuit 550 of the second signal processing circuit 5 will bedescribed. In the transmission ratio information storage section 556,information representing the value of a predetermined transmission ratio(for example, a gear ratio) of the power transmission device 2connecting the first encoder 3 and the second encoder 4 is stored inadvance as transmission ratio information. In the first resolutionstorage section 557, the resolution of the first position data detectioncircuit 561 is stored in advance as a first resolution. In the secondresolution storage section 558, the resolution of the second positiondata detection circuit 550 is stored in advance as a second resolution.

The second interpolation circuit 551 interpolates the second detectionsignal input from the second encoder 4 to detect the second positiondata. The second position detection circuit 552 calculates a value ofthe integer part of a value obtained by dividing a value which isobtained by multiplying the second position data detected by the secondinterpolation circuit 551 and the transmission ratio information readout from the transmission ratio information storage section 556 by thevalue of the second resolution read out from the second resolutionstorage section 558 as the rotation count and calculates a valueobtained by multiplying a value of the fractional part of the dividedvalue and the value of the first resolution read out from the firstresolution storage section 557 as the estimate. This estimate is theestimated position data of the accurate first position data detected bythe first encoder 3, calculated based on the second detection signaldetected by the second encoder 4.

For example, the second position detection circuit 552 calculates therotation count m and the estimate s using Equations 15 and 16 below.

m=INT(n(P2/R2))  (Equation 15)

s=R1×(n(P2/R2)−m)  (Equation 16)

In Equations 15 and 16, P2 is the second position data detected by thesecond interpolation circuit 551, R1 is the first resolution stored inthe first resolution storage section 557, R2 is the second resolutionstored in the second resolution storage section 558, and n is thetransmission ratio information read out from the transmission ratioinformation storage section 556. Moreover, INT is an operator thattruncates the fractional part and extracts only the integer part.

In this way, the second position data detection circuit 550 calculatesthe rotation count of the first encoder 3 and calculates the positiondata corresponding to the first position data as the estimate based onthe interpolated value of the second detection signal detected by thesecond encoder 4 and the transmission ratio information read out fromthe transmission ratio information storage section 556 by using thesecond interpolation circuit 551 and the second position detectioncircuit 552.

The transmission signal generation and output section 553 generates atransmission signal representing the value of the rotation count of theinput shaft 10 based on the estimate calculated by the second positiondetection circuit 552 and outputs the transmission signal to the secondposition data correction circuit 562. The transmission signal generationand output section 553 generates and outputs biphasic signals which aremultiple-rotation A and B signals which are first and second rectangularsignals of which the phases are different by 90°, for example, as thetransmission signal (see FIG. 11). The biphasic signals are preferablybiphasic rectangular signals which have a rectangular waveform so as tohave resistance to external noise or the like.

In FIG. 11, when the input shaft makes one rotation, namely when thefirst position data assumes the values from 0 to 131071, themultiple-rotation A signal and the multiple-rotation B signal change inthe signal pattern of H and L; H and H; L and H, and L and L. Here, Hand L are the potentials of an electrical signal and are, for example,high and low levels, respectively. Moreover, whenever the input shaftmakes one rotation, the multiple-rotation A signal and themultiple-rotation B signal repeat the above-described signal pattern.

The multiple-rotation A and B signals generated by the transmissionsignal generation and output section 553 have the following reliabilityin accordance with the transmission ratio n and the resolution R2 of thesecond position data detection circuit 550 in one rotation of the inputshaft.

The multiple-rotation A signal is H in a period where the residue ofR2/4n is 0 to 2n and is L in the other periods. On the other hand, themultiple-rotation B signal is H in a period where the residue of R2/4nis n to 3n and is L in the other periods.

For example, the transmission signal generation and output section 553generates the above-described multiple-rotation A and B signals in thefollowing manner. The transmission signal generation and output section553 outputs H for the multiple-rotation A signal when a value obtainedby subtracting 4n from a value obtained by multiplying the resolution R2of the second position data detection circuit 550 with the estimatecalculated by the second position detection circuit 552 is within therange of 0 to 2n, and outputs L for the multiple-rotation A signal whenthe value is outside the range. Moreover, the transmission signalgeneration and output section 553 outputs H for the multiple-rotation Bsignal when a value obtained by subtracting 4n from a value obtained bymultiplying the resolution R2 of the second position data detectioncircuit 550 with the estimate calculated by the second positiondetection circuit 552 is within the range of 1n to 3n, and outputs L forthe multiple-rotation B signal when the value is outside the range.

<Respective Configurations of First Signal Processing Circuit 6>

Next, the respective configurations of the first signal processingcircuit 6 will be described. In the transmission ratio informationstorage section 566, similarly to the transmission ratio informationstorage section 556, information representing the value of apredetermined transmission ratio (for example, a gear ratio) of thepower transmission device 2 connecting the first encoder 3 and thesecond encoder 4 is stored in advance as transmission ratio information.In the first resolution storage section 567, similarly to the firstresolution storage section 557, the resolution of the first positiondata detection circuit 561 is stored in advance as a first resolution.In the second resolution storage section 568, similarly to the secondresolution storage section 558, the resolution of the second positiondata detection circuit 550 is stored in advance as a second resolution.

The first position data detection circuit 561 detects first positiondata representing the angular position of the input shaft 10 throughfirst predetermined signal processing (interpolation) based on the firstdetection signal input from the first encoder 3.

The second position data correction circuit 562 corrects the secondposition data detected by the second position data detection circuit 550through predetermined correction processing based on the second positiondata and the first position data detected by the first position datadetection circuit 561.

The position data combination circuit 563 generates combined positiondata based on the value of the rotation count of the first encoder 3corrected by the second position data correction circuit 562 and thevalue of the first position data detected by the first position datadetection circuit 561. When combining the first position data detectedby the first position data detection circuit 561 and the second positiondata detected by the second position data detection circuit 550, theposition data combination circuit 563 generates the combined positiondata based on the transmission ratio information read out from thetransmission ratio information storage section 566.

Specifically, when combining the first position data detected by thefirst position data detection circuit 561 and the second position datadetected by the second position data detection circuit 550, the positiondata combination circuit 563 generates the combined position data by apredetermined calculation method based on the transmission ratioinformation read out from the transmission ratio information storagesection 566, the first resolution read out from the first resolutionstorage section 567, and the second resolution read out from the secondresolution storage section 568.

For example, the position data combination circuit 563 calculates thecombined position data using Equation 17 below.

Combined Position Data=P1+R1×INT(n×P2/R2)  (Equation 17)

Here, P1 is the first position data, P2 is the second position data, andn is a transmission ratio. Moreover, R1 is the resolution of the firstposition data detection circuit 561, and R2 is the resolution of thesecond position data detection circuit 550. Moreover, INT is an operatorthat truncates the fractional part and extracts only the integer part.

The position data combination circuit 563 calculates the integer part(INT) of a value obtained by multiplying a positional ratio (P2/R2)within one rotation of the second position data detection circuit 550with the gear ratio (n) and calculates a value obtained by adding thevalue of the first position data (P1) to a value obtained by multiplyingthe value (R1) of the resolution of the first position data detectioncircuit 550 with the value of the calculated integer part as thecombined position data using Equation 17.

Moreover, the position data combination circuit 563 outputs the combinedposition data generated by the position data combination circuit 563 tothe controller 8 through the communication line 9 using the externalcommunication circuit 565.

The external communication circuit 565 executes processing forcommunication with the controller 8 through the communication line 9.Moreover, the external communication circuit 565 stores the transmissionratio information received from the controller 8 through thecommunication line 9 in the transmission ratio information storagesection 566 and stores the transmission ratio information in thetransmission ratio information storage section 556 through the settingcontrol line 13.

Furthermore, the external communication circuit 565 stores the firstresolution received from the controller 8 through the communication line9 in the first resolution storage section 567 and stores the firstresolution in the first resolution storage section 557 through thesetting control line 13. In addition, the external communication circuit565 stores the second resolution received from the controller 8 throughthe communication line 9 in the second resolution storage section 568and stores the second resolution in the second resolution storagesection 558 through the setting control line 13.

The transmission ratio information storage sections 566 and 556 arenonvolatile memories, for example. Therefore, once the value of thetransmission ratio information stored in the transmission ratioinformation storage section 566 is set, it will not be erased even whenthe encoder system is powered off. According to this configuration, itis possible to broaden the choices for the power transmission device 2and the transmission ratio of the power transmission device 2 usable inthe encoder system.

Moreover, the first resolution storage sections 557 and 567 and thesecond resolution storage sections 558 and 568 are also nonvolatilememories, for example, similarly to the transmission ratio informationstorage sections 566 and 556. Therefore, it is similarly possible tobroaden the choices for the values of the resolutions of the first andsecond position data detection circuits 561 and 550 usable in theencoder system.

In the error correction value storage section 5620, an error correctionvalue for correcting the combined position data is stored in advance, inwhich the error correction value is obtained by driving the entire powertransmission device that rotates the output shaft 11 in advance in astate where the entire power transmission device is incorporated intothe encoder system.

The entire power transmission device may be, for example, a module inwhich the encoder system is incorporated. The module is the arm or thelike of an industrial robot, for example, and may be a component thatconstitutes a product, namely the industrial robot.

In the error correction value storage section 5620, an error angle(rotational angular position error) which is obtained by comparing adetection angle (rotation angle) based on the second position datadetected by the second encoder 4 and an angle measured with reference toa detection angle (rotation angle) based on the first position datadetected by the first encoder 3, and which is obtained from the entirepower transmission device is stored in advance as the error correctionvalue in a previous layer where the encoder system operated actually.

Specifically, in the error correction value storage section 5620, theerror correction value detected when the entire power transmissiondevice incorporated in the encoder system is driven in advance is storedin advance so as to be correlated with the second position data and thefirst position data.

The error correction circuit 5621 corrects the combined position data tobe generated by the position data combination circuit 563 based on theerror correction value read out from the error correction value storagesection 5620. Specifically, when the input shaft 10 is rotated, theerror correction circuit 5621 reads out the error correction valuecorrelated with the first position data detected by the first positiondata detection circuit 561 and the second position data detected by thesecond position data detection circuit 550 from the error correctionvalue storage section 5620 and corrects the combined position data to begenerated by the position data combination circuit 563 based on the readerror correction value.

<First Method of Obtaining Error Correction Value Stored in ErrorCorrection Value Storage Section 5620>

Here, a method of obtaining the error correction value stored in theerror correction value storage section 5620 and a method of storing theerror correction value in the error correction value storage section5620 will be described.

In general, in a power transmission device such as a gear and a beltpulley, an angular error in the rotation angle may occur due to theinfluence of the engagement error of the gear teeth, rotationaleccentricity of the pulley, a load fluctuation, and the like.

As described above, if the power transmission device has a rotationangle error, there is a problem in that it is unable to control themotor or the like with an accurate rotation angle even when a systemincluding the encoder system is controlled based on the angle of theoutput shaft 11 which is estimated through conversion from the angle ofthe input shaft 10.

In order to solve this problem, the detection angle of the first encoder3 on the input shaft 10 and the detection angle of the second encoder 4on the output shaft 11 are measured in advance while causing the outputshaft 11 to make at least one rotation. Then, the detection angle of thefirst encoder 3 on the input shaft 10 is compared with a theoreticalrotation angle (a rotation angle calculated based on a reduction ratio)of the input shaft 10 corresponding to the detection angle of the outputshaft 11 detected by the second encoder 4, whereby the error angle isdetected.

For example, in a calibration step before shipping the encoder system ofthe present embodiment, the error angle is measured usingspecial-purpose measuring equipment. Then, the error angle measuredusing the special-purpose measuring equipment is input from thecontroller 8 to the encoder system, and the external communicationcircuit 565 stores the error correction value δP in the error correctionvalue storage section 5620 so as to be correlated with the firstposition data detected by the first position data detection circuit 561and the second position data detected by the second position datadetection circuit 550.

The error correction value storage section 5620 is also a nonvolatilememory. Therefore, once the error correction value δP is stored in theerror correction value storage section 5620, even after the encodersystem is shipped, the encoder system can correct the combined positiondata to be generated by the position data combination circuit 563 basedon the error correction value δP stored in the error correction valuestorage section 5620.

Moreover, in the calibration step before shipping the encoder system, bymeasuring the actual error angle for each encoder system, it is possibleto correct the error for each encoder system.

FIG. 28 shows an example of the error angle of the input shaft 10 of thefirst encoder 3 with respect to the theoretical rotation angle of thefirst encoder 3 within one rotation of the second encoder 4.

That is, the error angle becomes the rotation angle error of the powertransmission device. Moreover, the rotation angle error is stored inadvance in the error correction value storage section 5620 as the errorcorrection value δP. At the time of driving the encoder system actually,the error correction circuit 5621 corrects the angle based on the errorcorrection value δP stored in the error correction value storage section5620 and transmits the corrected angle to the controller 8 so that thecombined position data can be calculated accurately.

For example, the error correction value δP is stored in advance in theerror correction value storage section 5620 so as to be correlated withthe value P2 of the second position data and the value P1 of the firstposition data. Here, it is assumed that the error correction value SP isan error correction value (δP2) for correcting the value P2 of thesecond position data.

When the combined position data is calculated by Equation 17, the errorcorrection circuit 5621 reads out the error correction value (δP2)corresponding to the value P2 of the second position data and the valueP1 of the first position data used in Equation 17 from the errorcorrection value storage section 5620 and corrects the value P2 of thesecond position data by adding the read error correction value (δP2) tothe value P2. Then, the position data combination circuit 563 calculatesthe combined position data based on the value P2 of the second positiondata corrected based on the error correction value (δP2).

That is, the position data combination circuit 563 generates thecombined position data using Equation 18 below.

Combined Position Data=P1+R1×INT(n×(P2+δP2)/R2)  (Equation 18)

In Equation 18, the term (P2+δP2) is a term that is corrected by theposition data combination circuit 563 in Equation 17 described above.

When calculating the combined position data using Equation 18, forexample, the error correction circuit 5621 reads out the recordingexecution device (δP2) corresponding to the value P2 of the secondposition data and the value P1 of the first position data from the errorcorrection value storage section 5620 and corrects the value P2 of thesecond position data corrected by the second position data correctioncircuit 562 based on the error correction value (δP2). Then, thecorrected value P2 of the second position data is output from the secondposition data correction circuit 562 to the position data combinationcircuit 563, and the position data combination circuit 563 calculatesthe combined position data using Equation 18 described above.

This method has features in that it can detect the error angle of thepower transmission device easily from the error angle which is obtainedby the two encoders of the second encoder 4 and the first encoder 3 withreference to the rotation angle of the first encoder 3. Showing from thesecond encoder 4, the first encoder 3 of which the resolution isincreased by the factor of the transmission ratio of the powertransmission device is used as a reference.

As described above, in the present embodiment, the error correctionvalue δP which is obtained by driving the entire power transmissiondevice that rotates the output shaft 11 in advance in a state where theentire power transmission device is incorporated into the encoder systemis stored in advance. Moreover, the error correction circuit 5621corrects the combined position data corrected by the position datacombination circuit 563 based on the error correction value δP read outfrom the error correction value storage section 5620. In this way, it ispossible to generate the combined position properly even when there is ashift (for example, a shift in the multiple-rotation count) between therotation of the input shaft 10 and the rotation of the output shaft 11.

<Second Method of Obtaining Error Correction Value Stored in ErrorCorrection Value Storage Section 5620>

FIG. 29 shows a second method of detecting the error angle with higherprecision. In the present embodiment, a high-precision absolute encoder31 which serves as an error detection reference is temporarily mountedinstead of the first encoder 3, and in this state, the rotation angleerror of the power transmission device is detected while causing theoutput shaft 11 to make at least one rotation similarly to the firstmethod described above. Moreover, the detected rotation angle error isstored in the error correction value storage section 5620 similarly tothe first method.

After that, the first encoder 3 serving as a product is mounted insteadof the high-precision absolute encoder 31 serving as the reference, thusassembling the product. Since a method of correcting the combinedposition data based on the error correction value δP stored in the errorcorrection value storage section 5620 at the time of driving the encodersystem actually is the same as the first method described above,description thereof will be omitted.

As described above, in the error correction value storage section 5620,an error angle which is obtained by comparing the detection angledetected by the second encoder 4 and an angle measured with reference tothe detection angle detected by the high-precision absolute encoder 31(absolute position reference detector) instead of the first encoder 3,and which is obtained from the entire power transmission device may bestored in advance as the error correction value δP.

This method has features in that it can detect the rotation angle erroreasily with high precision by using the special-purpose high-precisionabsolute encoder 31 at the time of manufacturing the device.

In the above-described embodiment, the rotation angle error of the powertransmission device when no load torque is applied to the output shaft11 has been described. However, when the magnitude of a load torque isunderstood under the actual use environment, by detecting the rotationangle error of the power transmission device in a state where the loadtorque is applied to the output shaft 11, it is possible to detect amore accurate rotation angle error. Moreover, in the case of using theabove-described planetary reduction gear, additional gears, pulleys,timing belts, and the like are used in order to further decelerate theoutput shaft. According to the present embodiment, it is possible tocorrect the motor angle considering the rotation angle error of theentire power transmission device including the pulleys and the like aswell as the error of the planetary reduction gear. Moreover, in thepresent embodiment, for example, since the first encoder 3 is disposedon the input shaft and the second encoder 4 is disposed on the outputshaft, it is possible to detect the rotation angle error (for example,the rotation angle error and the like of the output shaft) occurring dueto a load fluctuation or the like with high precision and to correct thecombined position data accurately.

The error correction circuit 5621 may read out the estimate estimated asthe first position data to be detected by the first position datadetection circuit 561 based on the second position data detected by thesecond position data detection circuit 550 and the error correctionvalue δP correlated with the second position data detected by the secondposition data detection circuit 550 from the error correction valuestorage section 5620 and correct the combined position data to begenerated by the position data combination circuit based on the readerror correction value δP.

For example, when the first position data has an abnormal value due to afailure in the first encoder 3 or the first position data detectioncircuit 561, the error correction circuit 5621 may use theabove-described estimate instead of the first position data as describedabove. The estimate is the estimate s calculated by Equation 16.

For example, the second position detection circuit 552 calculates theestimate s and transmits the calculated estimate s to the secondposition data correction circuit 562. As a method of transmitting theestimate s, for example, the transmission signal generation and outputsection 553 may transmit the estimate s to the second position datacorrection circuit 562 together with the rotation count m as a biphasicsinusoidal signal. Moreover, the error correction circuit 5621 reads outthe error correction value δP from the error correction value storagesection 5620 based on the estimate s received from the second positiondata correction circuit 562 and corrects the combined position data tobe generated by the position data combination circuit based on the readerror correction value δP.

Although the estimate s has been described to be output from the secondsignal processing circuit 5 to the first signal processing circuit 6 asthe biphasic sinusoidal signal, the transmission method is arbitrary,and for example, the estimate may be transmitted through a differentcommunication line from the communication line 12 and may be transmittedin an arbitrary transmission format.

In order to detect whether or not the first position data has anabnormal value, the first signal processing circuit 6 may include afailure detection circuit 5622 that detects an abnormality of the firstposition data, for example. It is assumed that the failure detectioncircuit 5622 receives the control signal for driving the motor 1 fromthe controller 8 using the external communication circuit 565 and isable to calculate the value that should be assumed by the first positiondata based on the control signal.

Moreover, the failure detection circuit 5622 compares the value of thefirst position data output from the first position data detectioncircuit 561 with the value that should be assumed by the first positiondata calculated based on the control signal from the controller 8, andwhen the two value are not identical, detects that the first positiondata is abnormal.

When the failure detection circuit 5622 has not detected an abnormalityof the first position data, the error correction circuit 5621 reads outthe error correction value δP correlated with the first position datadetected by the first position data detection circuit 561 and the secondposition data detected by the second position data detection circuit 550from the error correction value storage section 5620 and corrects thecombined position data to be generated by the position data combinationcircuit based on the read error correction value δP.

On the other hand, when the failure detection circuit 5622 has detectedan abnormality of the first position data, the error correction circuit5621 reads out the estimate estimated as the first position data to bedetected by the first position data detection circuit 561 based on thesecond position data detected by the second position data detectioncircuit 550 and the error correction value δP correlated with the secondposition data detected by the second position data detection circuit 550from the error correction value storage section 5620 and corrects thecombined position data to be generated by the position data combinationcircuit based on the read error correction value δP.

By doing so, the failure detection circuit 5622 can correct the combinedposition data to be generated by the position data combination circuiteven when the first position data has an abnormal value due to a failurein the first encoder 3 or the first position data detection circuit 561,for example.

Moreover, the position data combination circuit 563 may generate thecombined position data by Equation 19 below using the estimate sestimated as the first position data to be detected by the firstposition data detection circuit 561 based on the second position datadetected by the second position data detection circuit 550 instead ofthe first position data (P1) detected by the first position datadetection circuit 561.

Combined Position Data=s+R1×INT(n×(P2+δP2)/R2)  (Equation 19)

For example, when the failure detection circuit 5622 has not detected anabnormality of the first position data, the position data combinationcircuit 563 generates the combined position data by Equation 17 based onthe first position data detected by the first position data detectioncircuit 561.

On the other hand, the failure detection circuit 5622 has detected anabnormality of the first position data, the position data combinationcircuit 563 generates the combined position data by Equation 19 usingthe estimate s estimated as the first position data to be detected bythe first position data detection circuit 561 based on the secondposition data detected by the second position data detection circuit 550instead of the first S position data (P1) detected by the first positiondata detection circuit 561.

By doing so, the position data combination circuit 563 can generate thecombined position data even when the first position data has an abnormalvalue due to a failure in the first encoder 3 or the first position datadetection circuit 561, for example.

Returning to the description of FIG. 27, in the rotation count storagesection 564, the value of the rotation count of the input shaft 10detected by the second encoder 4 is stored. Moreover, the secondposition data correction circuit 562 detects the value of the rotationcount by increasing or decreasing the value of the rotation count storedin the rotation count storage section 564 by 1 in response to thereception of the transmission signal from the second signal processingcircuit 5.

In the rotation count storage section 564, the value of the rotationcount of the input shaft 10 detected by the second encoder 4 at thestartup time of the encoder system is stored. For example, when theencoder system is started up, the transmission signal generation andoutput section 553 of the second signal processing circuit 5 outputs amultiple-rotation signal corresponding to the rotation count, whichrepeats the signal pattern of the multiple-rotation A and B signalsdescribed using FIG. 11 at a cycle of 1 KHz as an initial value settingsignal. Moreover, the second position data correction circuit 562 storesa value corresponding to the initial value setting signal received fromthe transmission signal generation and output section 553 of the secondsignal processing circuit 5 in the rotation count storage section 564.As a result, the rotation count information is stored in the rotationcount storage section 564.

After that, the second position data correction circuit 562 increases ordecreases the value of the rotation count stored in the rotation countstorage section 564 in response to the reception of the transmissionsignal from the second signal processing circuit 5. Moreover, the errorcorrection circuit 5621 corrects the angular error of the powertransmission device. In this way, the value of the rotation count of theinput shaft 10 is detected based on the rotation of the output shaft 11.

<Details of Second Position Data Correction Circuit 562>

Next, the configuration of the second position data correction circuit562 will be described in further detail. For example, there is apossibility that a shift occurs between the first position datarepresenting the rotational position of the input shaft 10 and thesecond position data representing the rotational position of the outputshaft 11. This shift results, for example, from the engagement betweenthe input shaft 10 and the power transmission device 2 and theengagement between the power transmission device 2 and the output shaft11 and occurs physically.

Therefore, as shown in FIG. 9, there is a possibility that a shiftoccurs between the time when the rotation count (m) calculated based onthe second position data changes and the time when the first positiondata (P1) representing the rotational position of the input shaft 10changes. When there is such a shift, the position data combinationcircuit 563 is unable to generate the combined position data properly.Therefore, the second position data correction circuit 562 calculates acorrection value Δm and corrects the rotation count (m) by adding thecalculated correction value Δm to the rotation count as shown in FIG. 10so that the position data combination circuit 563 can generate thecombined position data properly even when there is such a shift.

Next, a rotation count correction method by the second position datacorrection circuit 562 will be described using FIGS. 9 and 10. In thisexample, a case in which the value of the first position data is 17 bitwill be described.

As shown in FIG. 9, the output shaft 11 rotates with the rotation of theinput shaft 10, and the rotation count m is calculated based on thevalue P2 of the second position data. Moreover, the value P1 of thefirst position data repeats the values from 0 to 131071 (=2¹⁷−1). Thatis, when the value P1 of the first position data repeats the values from0 to 131071 (=2¹⁷−1), the rotation count m changes in the order of 10,11, 12. There is a shift between the position of change (for example,the time when the value P1 of the first position data becomes 0) in theinput shaft rotation count detected based on the value P1 of the firstposition data and the time when the rotation count m changes.

As shown in FIG. 10, for example, when the value P1 of the firstposition data is within the range of 0 to 32767 (=2¹⁷×1/4−1), and thecalculated rotation count m is in the posterior half region, the secondposition data correction circuit 562 corrects the value of the rotationcount m by adding a correction value Δm (=1) to the value of therotation count m. Here, the calculated rotation count m being in theposterior half region means that the value of the calculated rotationcount m is actually m but is close to m+1.

Moreover, as shown in FIG. 10, for example, when the value P1 of thefirst position data is within the range of 98304 (=2¹⁷×3/4−1) to 131071(=2¹⁷−1), and the calculated rotation count m is in the anterior halfregion, the second position data correction circuit 562 corrects thevalue of the rotation count m by adding a correction value Δm (=−1) tothe value of the rotation count m. Here, the calculated rotation count mbeing in the anterior half region means that the value of the calculatedrotation count m is actually m but is close to m−1.

The determination as to whether the calculated rotation count m is inthe posterior half region or the anterior half region is made based onthe value of the estimate. For example, when the value of the estimatecalculated by the second position detection circuit 552 is smaller than0.5 (half cycle), the second position data correction circuit 562determines that the rotation count m is in the anterior half region.When the value of the estimate is equal to or larger than 0.5 (halfcycle), the rotation count m is determined to be in the posterior halfregion.

In FIG. 10, it was determined whether the rotational position of theinput shaft 10 detected based on the value of the rotation countdetected by the first encoder 3 is in the anterior 1/4 region (0 to32767) of the rotation in one rotation of the input shaft 10 or theposterior 1/4 region (98304 to 131071). However, in order to detect theshift, it may be determined whether the rotational position of the inputshaft 10 detected based on the value of the rotation count detected bythe first encoder 3 is in the anterior half region of the rotation inone rotation of the input shaft 10 or the posterior half region.

Therefore, the second position data correction circuit 562 may determinewhether the rotational position of the input shaft 10 estimated based onthe value of the estimate calculated by the second position detectioncircuit 552 is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region anddetermine whether the rotational position of the input shaft 10 detectedbased on the value of the rotation count detected by the first encoder 3is in the anterior half region of the rotation in one rotation of theinput shaft 10 or the posterior half region. Moreover, when the twodetermination results are different, the second position data correctioncircuit 562 may correct the value of the rotation count calculated bythe second position detection circuit 552.

Specifically, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 552 is in the posterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 561is in the anterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 562 correctsthe value of the rotation count calculated by the second positiondetection circuit 552 by adding 1 to the value of the rotation count.

On the other hand, when the rotational position of the input shaft 10estimated based on the value of the estimate calculated by the secondposition detection circuit 552 is in the anterior half region of therotation in one rotation of the input shaft 10, and the rotationalposition of the input shaft 10 detected based on the value of the firstposition data detected by the first position data detection circuit 561is in the posterior half region of the rotation in one rotation of theinput shaft 10, the second position data correction circuit 562 correctsthe value of the rotation count calculated by the second positiondetection circuit 552 by adding −1 to the value of the rotation count,namely by subtracting 1 from the value of the rotation count.

Then, the second position data correction circuit 562 determines whetherthe rotational position of the input shaft 10 corresponding to therotation count is in the anterior half region of the rotation in onerotation of the input shaft 10 or the posterior half region based on thetransmission signal input from the transmission signal generation andoutput section 553 of the second position data detection circuit 550 andcorrects the value of the rotation count.

In this example, a case in which the signal input to the second positiondata correction circuit 562 is a biphasic rectangular wave including themultiple-rotation A and B signals as shown in FIG. 11 will be described.

For example, as shown in FIG. 11, the multiple-rotation A and B signalschange in the signal pattern of H and L; H and H; L and H; and L and Lwhenever the input shaft makes one rotation. Therefore, when themultiple-rotation A and B signals are H and L, or H and H, respectively,the second position data correction circuit 562 determines that therotational position is in the anterior half region of the rotation inone rotation of the input shaft. On the other hand, when themultiple-rotation A and B signals are L and H, or L and L, respectively,the second position data correction circuit 562 determines that therotational position is in the posterior half region of the rotation inone rotation of the input shaft.

More specifically, when the multiple-rotation A and B signals are H andL, respectively, the second position data correction circuit 562determines that the rotational position is in the starting 1/4 region ofthe rotation in one rotation of the input shaft. Moreover, when themultiple-rotation A and B signals are L and L, respectively, the secondposition data correction circuit 562 determines that the rotationalposition is in the ending 1/4 region of the rotation in one rotation ofthe input shaft.

Moreover, the second position data correction circuit 562 detects thatthe input shaft has made one rotation by detecting that the inputmultiple-rotation A and B signals have changed sequentially in thesignal pattern of H and L; H and H; L and H; and L and L. On the otherhand, the second position data correction circuit 562 detects that theinput shaft has made one rotation in a reverse direction, namely −1rotation, by detecting that the input multiple-rotation A and B signalshave changed sequentially in the signal pattern of L and L; L and H; Hand H; and H and L.

In the description above, although the case in which the signal input tothe second position data correction circuit 562 is a biphasicrectangular wave including the multiple-rotation A and B signals asshown in FIG. 11 has been described, the same signal processing in thesecond position data correction circuit 562 is applied to a case inwhich the biphasic rectangular wave is a biphasic sinusoidal signal.

For example, in the case of the biphasic sinusoidal signal, the biphasicsinusoidal signal may be converted into a biphasic rectangular wave bythe internal section of the second position data correction circuit 562,and the second position data correction circuit 562 may execute thesignal processing described using FIGS. 9 and 10 based on the convertedbiphasic rectangular wave.

Moreover, the biphasic sinusoidal signal may be the same signal as thatused when outputting the estimate s from the second signal processingcircuit 5 to the first signal processing circuit 6. In this case, theposition data combination circuit 563 can also generate the combinedposition data using the value corrected by the failure detection circuit5622 and the second position data correction circuit 562.

Moreover, in the case of the biphasic sinusoidal signal, since it ispossible to output the estimate s from the second signal processingcircuit 5 to the first signal processing circuit 6, even when the firstposition data has an abnormal value, the position data combinationcircuit 563 can generate the combined position data by Equation 19described above using the estimate s instead of the first position data.

In the conventional art, there was a problem in that since the rotationangle error of a planetary reduction gear, for example, changes with thefluctuation of a load, it was not possible to correct the rotation angleaccurately.

In the conventional art, in general, there is a possibility that arotation angle error occurs between the rotation of the input shaft andthe rotation of the output shaft due to a load fluctuation, for example.Therefore, in the encoder system, there was a problem in that it isunable to accurately correct the rotation angle error occurring betweenthe rotation of the input shaft and the rotation of the output shaft.

According to the present embodiment, it is possible to provide anencoder system and a signal processing method capable of accuratelycorrecting the rotation angle error occurring between the rotation ofthe input shaft and the rotation of the output shaft.

According to the present embodiment, it is possible to accuratelycorrect the rotation angle error occurring between the rotation of theinput shaft and the rotation of the output shaft.

In the embodiment described using FIG. 27, although the error correctioncircuit 5621 has been described to be connected to the second positiondata correction circuit 562, a configuration having the same function asthe error correction circuit 5621 may be connected to the secondposition detection circuit 552 in the second signal processing circuit5. In such a configuration, after the second position data is correctedby the second position detection circuit 552; that is, a powertransmission error is corrected in the second signal processing circuit5, the corrected second position data may be transmitted to the secondposition data correction circuit 562.

As shown in FIG. 30, the first encoder 3 may include the first signalprocessing circuit 6 and the second signal processing circuit 5 whichare integrated with each other. For example, the second detection signaldetected by the second encoder 4 is input to the second interpolationcircuit 551 of the first and second signal processing circuits 6 and 5which are integrated with each other through the signal line 15 (seeFIG. 31).

Moreover, in this case, as shown in FIG. 31, the second positiondetection circuit 552 may output the calculated rotation count m and theestimate s to the second position data correction circuit 562.

In the configuration shown in FIGS. 30 and 31, the error correctioncircuit 5621 can also correct the combined position data to be generatedby the position data combination circuit 563 based on the errorcorrection circuit δP read out from the error correction value storagesection 5620. In this way, it is possible to generate the combinedposition properly even when there is a shift between the rotation of theinput shaft 10 and the rotation of the output shaft 11.

The first encoder 3 and the second encoder 4 may be a magnetic encoderor may be an optical encoder.

Moreover, the function of the error correction circuit 5621 may beprovided to the second position data correction circuit 562 or thesecond position detection circuit 552. Alternatively, the errorcorrection circuit 5621 may be integrated with the second position datacorrection circuit 562 or the second position detection circuit 552.

Moreover, in the description above, when the failure detection circuit5622 has detected an abnormality in the first position data, the errorcorrection circuit 5621 or the error correction circuit 5621 and theposition data combination circuit 563 have been described to use theestimate s of the first position data to be detected by the firstposition data detection circuit 561 estimated based on the secondposition data detected by the second position data detection circuit550, instead of using the first position data (P1) detected by the firstposition data detection circuit 561.

However, the present invention is not limited to this, and when thefailure detection circuit 5622 has detected an abnormality in the firstposition data, only the position data combination circuit 563 may usethe estimate s of the first position data to be detected by the firstposition data detection circuit 561 estimated based on the secondposition data detected by the second position data detection circuit550, instead of using the first position data (P1) detected by the firstposition data detection circuit 561.

That is, the position data combination circuit 563 may generate thecombined position data by Equation 20 below using the estimate s insteadof the first position data (P1).

Combined Position Data=s+R1×INT(n×P2/R2)  (Equation 20)

By doing so, for example, even when the error correction value SP is notstored in the error correction value storage section 5620, or theencoder system does not have the error correction circuit 5621, and thefirst position data has an abnormal value, the position data combinationcircuit 563 can generate the combined position data.

The same kinds of information are stored in the transmission ratioinformation storage sections 556 and 566, the first resolution storagesections 557 and 567, and the second resolution storage sections 558 and568, respectively. Therefore, the transmission ratio information storagesections 556 and 566, the first resolution storage sections 557 and 567,and the second resolution storage sections 558 and 568 may be configuredas an integrated section, respectively, and the respective integratedstorage sections may be provided in any one of the first and secondsignal processing circuits 6 and 5 or the encoder system. Moreover, thefirst and second signal processing circuits 6 and 5 may read outinformation from these respective integrated storage sections,respectively.

Moreover, the error correction value δP stored in the error correctionvalue storage section 5620 may include a plurality of error correctionvalues δP such as an acceleration, torque, and the like of the motor,and the plurality of error correction values δP may be selected asnecessary.

It is assumed that these storage sections and the error correction valuestorage section 5620 are configured by a nonvolatile memory such as ahard disk device, an optomagnetic disk device, or a flash memory, avolatile memory such as a read-only storage medium (for example,CD-ROM), or RAM (Random Access Memory), or a combination thereof.

The respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 shown in FIG. 27may be realized by special-purpose hardware and may be realized bymemories and microprocessors.

Moreover, the respective constituent circuits of the first signalprocessing circuit 6 and the second signal processing circuit 5 may berealized by special-purpose hardware. Furthermore, the respectiveconstituent circuits of the first signal processing circuit 6 and thesecond signal processing circuit 5 may be configured by memories andCPUs (Central Processing Unit), and programs for realizing the functionsof the respective constituent circuits of the first signal processingcircuit 6 and the second signal processing circuit 5 may be loaded intothe memories and executed, whereby the functions are realized.

While the embodiments of the present invention have been described indetail with reference to the drawings, the specific configuration is notlimited to the embodiments, and various changes and modifications may bemade without departing from the spirit of the present invention.

1. An encoder system comprising: a motor that rotates an input shaft; afirst absolute position encoder that is a single-rotation absoluteencoder and that outputs a first detection signal corresponding to apositional displacement in the rotation of the input shaft; a powertransmission device that rotates an output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft; asecond absolute position encoder that is a single-rotation absoluteencoder and that outputs a second detection signal corresponding to apositional displacement in the rotation of the output shaft; and asignal processing circuit that processes the first and second detectionsignals corresponding to the positional displacements detected by thefirst and second absolute position encoders, wherein the signalprocessing circuit includes: a first position data detection circuitthat detects first position data representing the positionaldisplacement in the rotation of the input shaft through firstpredetermined signal processing based on the first detection signalinput from the first absolute position encoder; a second position datadetection circuit that detects second position data representing thepositional displacement in the rotation of the output shaft throughsecond predetermined signal processing based on the second detectionsignal input from the second absolute position encoder; a position datacombination circuit that combines the first position data detected bythe first position data detection circuit and the second position datadetected by the second position data detection circuit to generatecombined position data representing the number of rotations of the inputshaft and the positional displacement within one rotation of the inputshaft; and a position data comparing and collating circuit that comparesand collates the first position data detected by the first position datadetection circuit and the second position data detected by the secondposition data detection circuit.
 2. The encoder system according toclaim 1, further comprising a transmission ratio information storagesection in which the predetermined transmission ratio of the powertransmission device is stored in advance as transmission ratioinformation, wherein the position data combination circuit combines thecombined position data based on a transmission ratio information readout from the transmission ratio information storage section whencombining the first position data detected by the first position datadetection circuit and the second position data detected by the secondposition data detection circuit.
 3. The encoder system according toclaim 2, wherein the position data comparing and collating circuit isconfigured to: calculate position data corresponding to the firstposition data to be detected by the first position data detectioncircuit as an estimate based on the second position data detected by thesecond position data detection circuit and the transmission ratioinformation read out from the transmission ratio information storagesection; calculate a difference between the calculated estimate and thefirst position data detected by the first position data detectioncircuit as an error estimate; and determine whether or not thecalculated error estimate is within a predetermined range of values,thus comparing and collating the first position data detected by thefirst position data detection circuit and the second position datadetected by the second position data detection circuit.
 4. The encodersystem according to claim 1, wherein the first absolute position encoderis an optical encoder, and wherein the second absolute position encoderis a magnetic encoder.
 5. The encoder system according to claim 4,wherein the first absolute position encoder outputs an absolute positiondetection signal and a first incremental signal as the first detectionsignal, wherein the second absolute position encoder outputs a secondincremental signal as the second detection signal, wherein the firstposition data detection circuit includes: an absolute position detectioncircuit that converts the absolute position detection signal input fromthe first absolute position encoder to output absolute position datarepresenting an absolute position in the rotation of the input shaft; afirst interpolation circuit that interpolates the first incrementalsignal input from the first absolute position encoder; and a positiondetection circuit that detects the first position data based on theabsolute position data output by the absolute position detection circuitand the first incremental signal interpolated by the first interpolationcircuit, wherein the second position data detection circuit includes asecond interpolation circuit that interpolates the second incrementalsignal input from the second absolute position encoder to detect thesecond position data.
 6. The encoder system according to claim 5,wherein the second interpolation circuit of the second position datadetection circuit performs the interpolation based on the transmissionratio information read out from the transmission ratio informationstorage section to detect the second position data when interpolatingthe second incremental signal input from the second absolute positionencoder.
 7. A signal processing method used in an encoder system whichincludes: a motor that rotates an input shaft; a first absolute positionencoder that is a single-rotation absolute encoder and that outputs afirst detection signal corresponding to a positional displacement in therotation of the input shaft; a power transmission device that rotates anoutput shaft at a predetermined transmission ratio in response to therotation of the input shaft; a second absolute position encoder that isa single-rotation absolute encoder and that outputs a second detectionsignal corresponding to a positional displacement in the rotation of theoutput shaft; and a signal processing circuit that processes the firstand second detection signals corresponding to the positionaldisplacements detected by the first and second absolute positionencoders, wherein the signal processing circuit comprises: a firstposition data detection step of detecting first position datarepresenting the positional displacement in the rotation of the inputshaft through first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection step of detecting second position datarepresenting the positional displacement in the rotation of the outputshaft through second predetermined signal processing based on the seconddetection signal input from the second absolute position encoder; aposition data combination step of combining the first position datadetected in the first position data detection step and the secondposition data detected in the second position data detection step togenerate combined position data representing the number of rotations ofthe input shaft and a positional displacement within one rotation of theinput shaft; and a position data comparing and collating step ofcomparing and collating the first position data detected in the firstposition data detection step and the second position data detected inthe second position data detection step.
 8. An encoder systemcomprising: a motor that rotates an input shaft; a first absoluteposition encoder that is a single-rotation absolute encoder and thatoutputs a first detection signal corresponding to an angular position ofthe input shaft; a power transmission device that rotates an outputshaft at a predetermined transmission ratio in response to the rotationof the input shaft; a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of the output shaft; a firstposition data detection circuit that detects first position datarepresenting the angular position of the input shaft through firstpredetermined signal processing based on the first detection signalinput from the first absolute position encoder; a second position datadetection circuit that detects second position data representing theangular position of the input shaft through second predetermined signalprocessing based on the second detection signal input from the secondabsolute position encoder; a transmission signal generation and outputsection that generates and outputs a transmission signal correspondingto the rotation of the input shaft based on the second position datadetected by the second position data detection circuit; and a positiondata combination circuit that measures a rotation count of the inputshaft based on the transmission signal input from the transmissionsignal generation and output section and combines the measured rotationcount and the first position data detected by the first position datadetection circuit to generate combined position data representing therotation count of the input shaft and the angular position of the inputshaft.
 9. The encoder system according to claim 8, wherein thetransmission signal generation and output section generates a pluralityof signals, of which one cycle corresponds to one rotation of the inputshaft, and of which the phases are different, as the transmissionsignal.
 10. The encoder system according to claim 8, wherein thetransmission signal is a biphasic rectangular wave of which one cyclecorresponds to one rotation of the input shaft.
 11. The encoder systemaccording to claim 10, further comprising a rotation count storagesection in which the rotation count of the input shaft is stored,wherein the position data combination circuit receives the transmissionsignal as the plurality of signals, detects an increment or a decrementof the number of rotations of the input shaft based on a combination ofthe plurality of received signals, and adds the detected increment ordecrement of the number of rotations to the value of the rotation countof the input shaft read out from the rotation count storage section,thus calculating the rotation count of the input shaft.
 12. The encodersystem according to claim 10, further comprising: a transmission-sideinitialization setting section that generates and outputs thetransmission signal for cycles corresponding to the rotation count ofthe input shaft based on the second position data detected by the secondposition data detection circuit when power is on; and a reception-sideinitialization setting section that stores the value of the rotationcount of the input shaft measured based on the received transmissionsignal for the cycles in the rotation count storage section uponreceiving the transmission signal for cycles corresponding to therotation count of the input shaft from the transmission-sideinitialization setting section.
 13. The encoder system according toclaim 8, wherein the transmission signal generation and output sectiongenerates and outputs serial data corresponding to the number ofrotations of the input shaft as the transmission signal.
 14. The encodersystem according to claim 8, further comprising a transmission ratioinformation storage section in which the predetermined transmissionratio of the power transmission device is stored in advance astransmission ratio information. wherein the second position datadetection circuit calculates the rotation count of the first absoluteposition encoder based on the interpolated value of the second detectionsignal detected by the second absolute position encoder and thetransmission ratio information read out from the transmission ratioinformation storage section and calculates the first position datadetected by the first absolute position encoder as an estimate based onthe second detection signal detected by the second absolute positionencoder, and wherein the transmission signal generation and outputsection generates and outputs the transmission signal based on theestimate calculated by the second position data detection circuit. 15.The encoder system according to claim 14, further comprising: a firstresolution storage section in which the resolution of the first positiondata detection circuit is stored in advance as a first resolution; and asecond resolution storage section in which the resolution of the secondposition data detection circuit is stored in advance as a secondresolution; wherein the second position data detection circuit includes:an interpolation circuit that interpolates the second detection signalinput from the second absolute position encoder to detect the secondposition data; and a position detection circuit that calculates a valueof the integer part of a value obtained by dividing a value which isobtained by multiplying the second position data detected by theinterpolation circuit and the transmission ratio information read outfrom the transmission ratio information storage section by the value ofthe second resolution read out from the second resolution storagesection as the rotation count and calculates a value obtained bymultiplying a value of the fractional part of the divided value and thevalue of the first resolution read out from the first resolution storagesection as the estimate.
 16. The encoder system according to claim 15,wherein the second absolute position encoder outputs a biphasicsinusoidal signal, which is made up of two sinusoidal signals of whichone cycle corresponds to one rotation of the output shaft and of whichthe phases are different by an amount of a predetermined phase, as thesecond detection signal, wherein the interpolation circuit of the secondposition data detection circuit is configured to: when the value of thefirst signal of the biphasic sinusoidal signal is larger than that ofthe second signal, detect the second position data based on a valueobtained by dividing the second signal by the first signal; and when thevalue of the first signal is smaller than that of the second signal,detect the second position data based on a value obtained by dividingthe first signal by the second signal.
 17. The encoder system accordingto claim 16, further comprising a conversion information storage sectionin which the second detection signal and the second position data arestored in advance in a correlated manner, wherein the interpolationcircuit of the second position data detection circuit reads out secondposition data corresponding to the second detection signal output by thesecond absolute position encoder from the conversion information storagesection to detect the second position data.
 18. The encoder systemaccording to claim 17, wherein in the conversion information storagesection, when the value of the first signal of the biphasic sinusoidalsignal is larger than that of the second signal, the value obtained bydividing the second signal by the first signal and the second positiondata corresponding to the divided value are stored in advance, and whenthe value of the first signal is smaller than that of the second signal,the value obtained by dividing the first signal by the second signal andthe second position data corresponding to the divided value are storedin advance.
 19. The encoder system according to claim 17, wherein thesecond detection signal and the second position data for only one phaseinterval are stored in advance in the conversion information storagesection in a correlated manner, and wherein the interpolation circuit ofthe second position data detection circuit determines which phaseinterval the rotational position of the output shaft corresponds to,among a plurality of phase intervals corresponding to one rotation ofthe output shaft, and calculates second position data in one rotation ofthe rotation of the output shaft based on a predetermined referencephase corresponding to the determined phase interval and the secondposition data in one phase interval read out from the conversioninformation storage section to detect the second position data.
 20. Theencoder system according to claim 8, further comprising a secondposition data correction circuit that measures a rotation count of theinput shaft based on the transmission signal input from the transmissionsignal generation and output section and corrects the measured rotationcount through predetermined correction processing based on the measuredrotation count and the first position data detected by the firstposition data detection circuit, wherein the position data combinationcircuit combines the rotation count corrected by the second positiondata correction circuit and the first position data detected by thefirst position data detection circuit to generate the combined positiondata.
 21. The encoder system according to claim 20, wherein the secondposition data correction circuit is configured to: correct the rotationcount by adding 1 to the value of the rotation count when the rotationalposition of the input shaft estimated by the value of the calculatedestimate is in a posterior half region of the rotation in one rotationof the input shaft, and the rotational position of the input shaftdetected by the first position data detected by the first position datadetection circuit is in an anterior half region of the rotation in onerotation of the input shaft; and correct the rotation count bysubtracting 1 from the value of the rotation count when the rotationalposition of the input shaft estimated by the value of the calculatedestimate is in an anterior half region of the rotation in one rotationof the input shaft, and the rotational position of the input shaftdetected by the first position data detected by the first position datadetection circuit is in a posterior half region of the rotation in onerotation of the input shaft.
 22. The encoder system according to claim20, wherein the transmission signal generation and output sectiongenerates a transmission signal which represents the value of therotation count and which represents whether the rotational position ofthe input shaft corresponding to the rotation count is in the anteriorhalf region of the rotation in one rotation of the input shaft or theposterior half region based on the calculated estimate and outputs thetransmission signal to the second position data correction circuit, andwherein the second position data correction circuit determines whetherthe rotational position of the input shaft corresponding to the rotationcount is in the anterior half region of the rotation in one rotation ofthe input shaft or the posterior half region based on the transmissionsignal input from the transmission signal generation and output sectionof the second position data detection circuit and corrects the value ofthe rotation count.
 23. The encoder system according to claim 8, whereina first processing circuit having at least the first position datadetection circuit includes a first external communication circuit thatoutputs the first position data detected by the first position datadetection circuit to a high-order device through a first communicationline, wherein a second processing circuit having at least the secondposition data correction circuit includes a second externalcommunication circuit that outputs the second position data corrected bythe second position data correction circuit to the high-order devicethrough a second communication line, and wherein the first processingcircuit and the second processing circuit are formed on differentsubstrates.
 24. A signal processing method used in an encoder systemwhich includes: a motor that rotates an input shaft; a first absoluteposition encoder that is a single-rotation absolute encoder and thatoutputs a first detection signal corresponding to an angular position ofthe input shaft; a power transmission device that rotates an outputshaft at a predetermined transmission ratio in response to the rotationof the input shaft; and a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of the output shaft, themethod comprising: detecting first position data representing theangular position of the input shaft through first predetermined signalprocessing based on the first detection signal input from the firstabsolute position encoder; detecting second position data representingthe angular position of the input shaft through second predeterminedsignal processing based on the second detection signal input from thesecond absolute position encoder; generating and outputting atransmission signal corresponding to the rotation of the input shaftbased on the second position data detected by the second position datadetection circuit; and measuring a rotation count of the input shaftbased on the input transmission signal and combining the measuredrotation count and the first position data detected by the firstposition data detection circuit to generate combined position datarepresenting the rotation count of the input shaft and the angularposition of the input shaft.
 25. A transmission signal generation andoutput device used in an encoder system which includes: a motor thatrotates an input shaft; a first absolute position encoder that is asingle-rotation absolute encoder and that outputs a first detectionsignal corresponding to an angular position of the input shaft; a powertransmission device that rotates an output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft; asecond absolute position encoder that is a single-rotation absoluteencoder and that outputs a second detection signal corresponding to anangular position of the output shaft, in which the encoder systemcombines the first position data detected by the first position datadetection circuit and a transmission signal input thereto to generatecombined position data representing the rotation count of the inputshaft and the angular position of the input shaft, wherein thetransmission signal generation and output device generates and outputs atransmission signal corresponding to the rotation of the input shaftbased on the second position data detected by the second position datadetection circuit.
 26. An encoder system comprising: a motor thatrotates an input shaft; a first absolute position encoder that is asingle-rotation absolute encoder and that outputs a first detectionsignal corresponding to an angular position of the input shaft; a powertransmission device that rotates an output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft; asecond absolute position encoder that is a single-rotation absoluteencoder and that outputs a second detection signal corresponding to anangular position of the output shaft; a first position data detectioncircuit that detects first position data representing the angularposition of the input shaft through first predetermined signalprocessing based on the first detection signal input from the firstabsolute position encoder; a second position data detection circuit thatdetects second position data representing the angular position of theinput shaft through second predetermined signal processing based on thesecond detection signal input from the second absolute position encoder;a position data combination circuit that combines the first positiondata detected by the first position data detection circuit and thesecond position data detected by the second position data detectioncircuit to generate combined position data representing amultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft; and a rotation directiondetection section that detects whether a rotation direction of the inputshaft detected based on the displacement of the first position data anda rotation direction of the output shaft detected based on thedisplacement of the second position data are the same directions orreverse directions.
 27. The encoder system according to claim 26,further comprising a communication section that receives informationrepresenting whether the rotation direction of the input shaft and therotation direction of the output shaft are the same directions or thereverse directions as a control signal, wherein the rotation directiondetection section detects whether the rotation direction of the inputshaft and the rotation direction of the output shaft are the samedirections or the reverse directions in response to reception of thecontrol signal by the communication section.
 28. The encoder systemaccording to claim 26, further comprising a power supply monitoringcircuit that detects supply of power, wherein the rotation directiondetection section detects whether the rotation direction of the inputshaft and the rotation direction of the output shaft are the samedirections or the reverse directions when the power supply monitoringcircuit has detected the supply of power.
 29. The encoder systemaccording to claim 26, further comprising a rotation directioninformation storage section in which the information representingwhether the rotation direction of the input shaft and the rotationdirection of the output shaft are the same directions or the reversedirections is stored in advance as rotation direction information,wherein the rotation direction detection section is configured to: whenthe rotation direction information read out from the rotation directioninformation storage section represents that the rotation direction ofthe input shaft and the rotation direction of the output shaft are thesame directions, detect whether or not the detected rotation directionof the input shaft and the detected rotation direction of the outputshaft are the same directions; and when the rotation directioninformation read out from the rotation direction information storagesection represents that the rotation direction of the input shaft andthe rotation direction of the output shaft are the reverse directions,detect whether or not the detected rotation direction of the input shaftand the detected rotation direction of the output shaft are the reversedirections.
 30. The encoder system according to claim 29, wherein thecommunication section receives the setting information representingwhether the rotation direction of the input shaft and the rotationdirection of the output shaft are the same direction or the reversedirections, and the encoder system further comprises a rotationdirection information setting section that stores the settinginformation received by the communication section in the rotationdirection information storage section as the rotation directioninformation.
 31. The encoder system according to claim 29, furthercomprising a controller that controls the rotation of the motor, whereinthe rotation direction detection section is configured to: when therotation direction information read out from the rotation directioninformation storage section represents that the rotation direction ofthe input shaft and the rotation direction of the output shaft are thesame directions, and the detection result shows that the rotationdirection of the input shaft and the rotation direction of the outputshaft are not the same directions, transmit the detection result to thecontroller as an abnormality signal; and when the rotation directioninformation read out from the rotation direction information storagesection represents that the rotation direction of the input shaft andthe rotation direction of the output shaft are the reverse directions,and the detection result shows that the rotation direction of the inputshaft and the rotation direction of the output shaft are not the reversedirections, transmit the detection result to the controller as anabnormality signal, and wherein the controller stops the rotation of themotor in response to reception of the abnormality signal.
 32. Theencoder system according to any claim 26, further comprising atransmission signal generation and output section that generates andoutputs a transmission signal which is a biphasic signal correspondingto the rotation of the input shaft based on the second position datadetected by the second position data detection circuit, wherein therotation direction detection section receives the transmission signalreceived from the transmission signal generation and output section anddetects the rotation direction of the output shaft based on the receivedtransmission signal.
 33. The encoder system according to claim 32,wherein the transmission signal generation and output section generatesand outputs a transmission signal which is a biphasic signal changingfor a predetermined plural number of times corresponding to one rotationof the input shaft.
 34. The encoder system according to claim 26,further comprising a transmission signal generation and output sectionthat generates and outputs a transmission signal which is serial datacorresponding to the rotation of the input shaft based on the secondposition data detected by the second position data detection circuit,wherein the rotation direction detection section receives thetransmission signal received from the transmission signal generation andoutput section and detects the rotation direction of the output shaftbased on the received transmission signal.
 35. The encoder systemaccording to claim 26, wherein a first processing circuit having atleast the first position data detection circuit includes a firstexternal communication circuit that outputs the first position datadetected by the first position data detection circuit to a high-orderdevice through a first communication line, wherein a second processingcircuit having at least the second position data correction circuitincludes a second external communication circuit that outputs the secondposition data corrected by the second position data correction circuitto the high-order device through a second communication line, andwherein the first processing circuit and the second processing circuitare formed on different substrates.
 36. A signal processing method usedin an encoder system which includes: a motor that rotates an inputshaft; a first absolute position encoder that is a single-rotationabsolute encoder and that outputs a first detection signal correspondingto an angular position of the input shaft; a power transmission devicethat rotates an output shaft at a predetermined transmission ratio inresponse to the rotation of the input shaft; and a second absoluteposition encoder that is a single-rotation absolute encoder and thatoutput is a second detection signal corresponding to an angular positionof the output shaft, the method comprising: a first position datadetection step of detecting first position data representing the angularposition of the input shaft through first predetermined signalprocessing based on the first detection signal input from the firstabsolute position encoder; a second position data detection step ofdetecting second position data representing the angular position of theinput shaft through second predetermined signal processing based on thesecond detection signal input from the second absolute position encoder;a position data combination step of combining the first position datadetected in the first position data detection step and the secondposition data detected in the second position data detection step togenerate combined position data representing a multiple-rotation countof the input shaft and the angular position within one rotation of theinput shaft; and a rotation direction detection step of detectingwhether a rotation direction of the input shaft detected based on thedisplacement of the first position data and a rotation direction of theoutput shaft detected based on the displacement of the second positiondata are the same directions or reverse directions.
 37. An encodersystem comprising: a motor that rotates an input shaft; a controllerthat controls the rotation of the motor using a rotation control signal;a first absolute position encoder that is a single-rotation absoluteencoder and that outputs a first detection signal corresponding to anangular position of the input shaft; a power transmission device thatrotates an output shaft at a predetermined transmission ratio inresponse to the rotation of the input shaft; a second absolute positionencoder that is a single-rotation absolute encoder and that outputs asecond detection signal corresponding to an angular position of theoutput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection circuit that detects second position datarepresenting the angular position of the input shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; a position datacombination circuit that combines the first position data detected bythe first position data detection circuit and the second position datadetected by the second position data detection circuit to generatecombined position data representing a multiple-rotation count of theinput shaft and the angular position within one rotation of the inputshaft; and a failure detection section that compares an input shaftangular position which is the angular position of the input shaftcalculated based on the rotation control signal from the controller andthe first position data detected by the first position data detectioncircuit and compares an output shaft angular position which is theangular position of the output shaft calculated based on the rotationcontrol signal from the controller and the second position data detectedby the second position data detection circuit to detect a failure inaccordance with a combination of the comparison results.
 38. The encodersystem according to claim 37, wherein the failure detection section isconfigured to: detect whether or not the input shaft angular positionand the first position data are identical and detect whether or not theoutput shaft angular position and the second position data areidentical; when the input shaft angular position and the first positiondata are not identical, and the output shaft angular position and thesecond position data are identical, output a signal to the controller,the signal representing that an input shaft-side device which is one ora combination of the first absolute position encoder and the firstposition data detection circuit has a failure; and when the input shaftangular position and the first position data are identical, and theoutput shaft angular position and the second position data are notidentical, output a signal to the controller, the signal representingthat an output shaft-side device which is one or a combination of thepower transmission device, the second absolute position encoder and thesecond position data detection circuit has a failure.
 39. The encodersystem according to claim 38, wherein the failure detection sectionoutputs the signal representing a failure to the controller when theinput shaft angular position and the first position data are notidentical, and the output shaft angular position and the second positiondata are not identical.
 40. The encoder system according to claim 38,wherein the failure detection section is configured to: when detectingwhether or not the input shaft angular position and the first positiondata are identical and whether or not the output shaft angular positionand the second position data are identical, detect that the input shaftangular position and the first position data are identical if adifference therebetween is equal to or smaller than a firstpredetermined allowable amount, and detect that they are not identicalif the difference is not equal to or smaller than the first allowableamount; and detect that the output shaft angular position and the secondposition data are identical if a difference therebetween is equal to orsmaller than a second predetermined allowable amount, and detect thatthey are not identical if the difference is not equal to or smaller thanthe second allowable amount.
 41. The encoder system according to claim37, further comprising a transmission ratio information storage sectionin which the predetermined transmission ratio of the power transmissiondevice is stored in advance as transmission ratio information, whereinthe failure detection section is configured to: calculate position datacorresponding to the first position data to be detected by the firstposition data detection circuit as an estimate based on the secondposition data detected by the second position data detection circuit andthe transmission ratio information read out from the transmission ratioinformation storage section; calculate a difference between thecalculated estimate and the first position data detected by the firstposition data detection circuit as an error estimate; and determinewhether or not the calculated error estimate is within a predeterminedrange of values and output a signal to the controller, the signalrepresenting that the first position data detected by the first positiondata detection circuit and the second position data detected by thesecond position data detection circuit are not identical when thedetermination result shows that the calculated error estimate is notwithin the predetermined range of values.
 42. The encoder systemaccording to claim 37, wherein a first processing circuit having atleast the first position data detection circuit includes a firstexternal communication circuit that outputs the first position datadetected by the first position data detection circuit to a high-orderdevice through a first communication line, wherein a second processingcircuit having at least the second position data correction circuitincludes a second external communication circuit that outputs the secondposition data corrected by the second position data correction circuitto the high-order device through a second communication line, andwherein the first processing circuit and the second processing circuitare formed on different substrates.
 43. A signal processing method usedin an encoder system which includes: a motor that rotates an inputshaft; a controller that controls the rotation of the motor using arotation control signal; a first absolute position encoder that is asingle-rotation absolute encoder and that outputs a first detectionsignal corresponding to an angular position of the input shaft; a powertransmission device that rotates an output shaft at a predeterminedtransmission ratio in response to the rotation of the input shaft; asecond absolute position encoder that is a single-rotation absoluteencoder and that outputs a second detection signal corresponding to anangular position of the output shaft; a first position data detectioncircuit that detects first position data representing the angularposition of the input shaft through first predetermined signalprocessing based on the first detection signal input from the firstabsolute position encoder; a second position data detection circuit thatdetects second position data representing the angular position of theoutput shaft through second predetermined signal processing based on thesecond detection signal input from the second absolute position encoder;and a signal processing section that processes the rotation controlsignal from the controller, the first position data detected by thefirst position data detection circuit, and the second position datadetected by the second position data detection circuit, wherein thesignal processing section comprises: a position data combination step ofcombining the first position data detected by the first position datadetection circuit and the second position data detected by the secondposition data detection circuit to generate combined position datarepresenting a multiple-rotation count of the input shaft and theangular position within one rotation of the input shaft; and a failuredetection step of comparing an input shaft angular position which is theangular position of the input shaft calculated based on the rotationcontrol signal from the controller and the first position data detectedby the first position data detection circuit and comparing an outputshaft angular position which is the angular position of the output shaftcalculated based on the rotation control signal from the controller andthe second position data detected by the second position data detectioncircuit to detect a failure in accordance with a combination of thecomparison results.
 44. An encoder system comprising: a first absoluteposition encoder that is a single-rotation absolute encoder and thatoutputs a first detection signal corresponding to an angular position ofa rotating input shaft; a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of an output shaft rotatingat a predetermined transmission ratio in response to the rotation of theinput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; asecond position data detection circuit that detects second position datarepresenting the angular position of the input shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder; a position datacombination circuit that combines the first position data and the secondposition data to generate combined position data representing amultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft; an error correction valuestorage section in which an error correction value for correcting thecombined position data is stored in advance, the error correction valuebeing a value which is obtained by driving an entire power transmissiondevice that rotates the output shaft in advance in a state where theentire power transmission device is incorporated into the encodersystem; and an error correction circuit that corrects the combinedposition data generated by the position data combination circuit basedon the error correction value read out from the error correction valuestorage section.
 45. The encoder system according to claim 44, whereinthe error correction value includes an error angle which is obtained bycomparing a detection angle based on the second position data detectedby the second absolute position encoder and an angle measured withreference to a detection angle based on the first position data detectedby the first absolute position encoder.
 46. The encoder system accordingto claim 44, wherein the error correction value includes an error anglewhich is obtained by comparing a detection angle based on the secondposition data detected by the second absolute position encoder and anangle measured with reference to a detection angle based on the firstposition data which is detected by a high-precision absolute positionreference detector instead of the first absolute position encoder. 47.The encoder system according to claim 44, wherein the error correctionvalue detected by driving the entire power transmission deviceincorporated into the encoder system in advance is stored in advance inthe error correction value storage section so as to be correlated to thesecond position data and the first position data, and wherein the errorcorrection circuit corrects the combined position data to be generatedby the position data combination circuit based on the error correctionvalue read out from the error correction value storage section.
 48. Theencoder system according to claim 44, wherein the error correctioncircuit reads out the error correction value correlated to the secondposition data and the estimate estimated as the first position databased on the second position data from the error correction valuestorage section and corrects the combined position data to be generatedby the position data combination circuit based on the read errorcorrection value.
 49. The encoder system according to claim 47, furthercomprising a failure detection circuit that detects an abnormality ofthe first position data, wherein the error correction circuit isconfigured to: when the failure detection circuit has not detected anabnormality of the first position data, read out the error correctionvalue correlated to the first position data and the second position datafrom the error correction value storage section and correct the combinedposition data to be generated by the position data combination circuitbased on the read error correction value; and when the failure detectioncircuit has detected an abnormality of the first position data, read outthe error correction value correlated to the second position data andthe estimate estimated as the first position data based on the secondposition data from the error correction value storage section andcorrect the combined position data to be generated by the position datacombination circuit based on the read error correction value.
 50. Theencoder system according to claim 44, wherein the position datacombination circuit combines the second position data and the estimateestimated as the first position data based on the second position datato generate the combined position data representing themultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft.
 51. A signal processing methodused in an encoder system which includes: a first absolute positionencoder that is a single-rotation absolute encoder and that outputs afirst detection signal corresponding to an angular position of arotating input shaft; a second absolute position encoder that is asingle-rotation absolute encoder and that outputs a second detectionsignal corresponding to an angular position of an output shaft rotatingat a predetermined transmission ratio in response to the rotation of theinput shaft; a first position data detection circuit that detects firstposition data representing the angular position of the input shaftthrough first predetermined signal processing based on the firstdetection signal input from the first absolute position encoder; and asecond position data detection circuit that detects second position datarepresenting the angular position of the output shaft through secondpredetermined signal processing based on the second detection signalinput from the second absolute position encoder, in which: a positiondata combination circuit combines the first position data and the secondposition data to generate combined position data representing amultiple-rotation count of the input shaft and the angular positionwithin one rotation of the input shaft; and an error correction circuitcorrects the combined position data to be generated by the position datacombination circuit based on an error correction value read out from anerror correction value storage section in which the error correctionvalue for correcting the combined position data is stored in advance,the error correction value being a value which is obtained by driving anentire power transmission device that rotates the output shaft inadvance in a state where the entire power transmission device isincorporated into the encoder system.
 52. An encoder system comprising:a first single-rotation absolute encoder that outputs a first signalcorresponding to an angular position of a first rotatable shaft; a powertransmission device that transmits the power of the first shaft to asecond rotatable shaft with a predetermined transmission ratio; a secondsingle-rotation absolute encoder that outputs a second signalcorresponding to an angular position of the second shaft; and a signalprocessing section that generates data related to the rotation count ofthe first shaft based on at least the first signal and the secondsignal.